Catchup vs Catch Up Which Form Is Correct 2026 Guide

English has a funny habit of making simple ideas look harder than they are. The Catchup vs Catch Up question is a good example. These forms sound almost identical in speech yet they serve different purposes in writing. The most common point of confusion is the difference between Catch Up, the standard phrasal verb, and Catchup, a one word form mainly associated with the less common spelling of ketchup. Related phrases such as Catch Up With, Catch Up On, Catch Up To, and Catch Up Meaning also appear frequently in everyday English.

If you mean reaching someone who is ahead, becoming current with missed work, learning recent information, or talking with someone to exchange news, use Catch Up as two words. For example, you can catch up with a friend, catch up on homework, or catch up on the latest news.

The one word Catchup has a different role. Major dictionaries recognize it as a less common spelling of ketchup. A related noun for a meeting or the process of reaching the same level is normally written as a hyphenated form in dictionary entries.

Understanding this small spelling difference can save you from an easy editing mistake. It also helps you recognize the grammar behind common phrasal verbs instead of relying only on how a phrase sounds.

Quick Answer

Use Catch Up when you mean to reach someone, become current, complete missed work, or exchange recent news. Catchup is mainly a less common spelling of ketchup. The related noun for a meeting or reaching the same level is commonly written as a hyphenated form in major dictionaries.

Catchup vs Catch Up At a Glance Comparison

Feature	Catchup	Catch up
Correct spelling for the verb	No	Yes
Main modern meaning	Usually a variant spelling of ketchup	Reach someone or get current
Meaning related to catching up	Not normally as a verb	Yes
Part of speech	Noun in its sauce meaning	Phrasal verb
Word type	One word	Two word phrasal verb
Pronunciation	Usually like ketchup	Same spoken sound
Origin	Connected to the history of ketchup	Built from catch and up
Grammar role	Noun when it means sauce	Verb phrase when it means reach or update yourself
Formality	Uncommon as a spelling for ketchup	Standard and widely used
Frequency	Uncommon	Very common
Typical context	Food and condiment terminology	Conversation work school news travel and everyday writing
Example	The recipe calls for catchup and mustard.	I need to catch up on my reading.

There is one important complication. English also has a noun referring to the process of reaching the same level or a meeting where people exchange recent news. Major dictionaries generally write that noun as a hyphenated form. Because the focus here is the exact one word form catchup versus the two word verb catch up, the safest practical rule is simple: use catch up for the verb. Do not turn the verb into catchup. (Oxford Learner’s Dictionaries)

Catchup vs Catch Up Which Word Should You Use

If your sentence contains an action such as getting current with work or reaching someone who is ahead, use catch up.

Consider these sentences.

I need to catch up on my emails.

She ran faster to catch up with her brother.

We spent the weekend catching up on the latest news.

The smaller company is trying to catch up with its competitors.

In every example, catch up functions as a phrasal verb. The two parts work together to create a meaning that is different from the basic meaning of catch by itself. Oxford lists catch up as a phrasal verb and gives meanings that include reaching someone ahead of you, reaching the same level, doing missed work, and finding out recent information. (Oxford Learner’s Dictionaries)

The one word catchup is not the normal spelling for these meanings.

There is an important dictionary detail that can trip up even careful writers. Merriam Webster lists catchup as a less common spelling of ketchup. It also separately recognizes the noun and adjective related to catching up. Cambridge likewise lists catchup as a US noun meaning a variant spelling of ketchup. (Merriam-Webster)

So the safest editorial rule is this.

Use catch up for the verb.

Use the standard noun spelling recommended by your style guide when you mean a meeting or the process of reaching the same level.

Treat catchup as a food spelling rather than as the normal verb spelling.

Understanding Catchup vs Catch Up

Catch up is a phrasal verb. A phrasal verb combines a main verb with another short word that changes or completes its meaning.

The verb catch can mean many things. You can catch a ball. Catch a bus, catch a cold, catch someone doing something. Add up and you get a different expression.

When you catch up with someone who is ahead, you reach them.

Use catch up on work, you do work that you did not complete earlier.

When you catch up on the news, you learn information that you missed.

When you catch up with a friend, you exchange news and talk about what has happened since you last met.

Oxford and Cambridge both document these uses. (Oxford Learner’s Dictionaries)

Catch Up With Someone

Use catch up with when the idea involves reaching a person or sometimes reaching the same level as another person or thing.

I walked faster so I could catch up with my friends.

She stayed late to catch up with her coworkers.

The company is trying to catch up with its larger competitors.

The expression can also describe a consequence finally reaching someone.

His past mistakes eventually caught up with him.

That last meaning is slightly different. It does not mean that someone physically reached another person. It means that a problem or consequence eventually affected someone. Oxford lists this use under catch up with as well. (Oxford Learner’s Dictionaries)

Catch Up On Something

Use catch up on when you need to complete or learn something you missed.

I need to catch up on my reading.

She spent Sunday catching up on paperwork.

I watched the recordings to catch up on the lessons I missed.

We stayed home to catch up on the latest episodes.

This pattern is especially common with work school entertainment news and personal information. Oxford specifically defines catch up on as spending extra time doing something you did not do earlier or finding out about things that happened. (Oxford Learner’s Dictionaries)

Catch Up To Someone

In American English, catch up to someone or something is also common.

I ran faster to catch up to the group.

The new model is finally catching up to its competitors.

The form with with is also standard.

I ran faster to catch up with the group.

There can be small regional preferences in preposition choice. The important point is that the verb itself remains two separate words.

Catch Up In Conversation

Catch up can also describe a social conversation.

I called my sister so we could catch up.

Let’s meet for coffee and catch up.

We had lunch and caught up on everything.

This meaning has become especially common in casual American English. Cambridge describes the verb as talking with someone you know in order to exchange news or information. (Cambridge Dictionary)

Understanding Catchup vs Catch Up

The one word form creates confusion because it has a legitimate dictionary history. But its most straightforward dictionary meaning has nothing to do with the verb phrase catch up.

Catchup can be a less common spelling of ketchup.

Merriam Webster lists it as a variant of ketchup. Cambridge also defines it as another spelling of ketchup. (Merriam-Webster)

For example.

The burger came with catchup and mustard.

The old recipe calls for catchup.

That spelling is unusual in modern American writing. Most readers expect ketchup.

So if you write I need to catchup on work, your reader may recognize your intended meaning from context. Still, the spelling is wrong for standard edited English.

The distinction is worth remembering because catchup and catch up can sound identical in ordinary speech. Writing makes the difference visible.

The Biggest Differences between Catchup vs Catch Up Explained

Spelling

The most important difference is simple.

Catch up is two words when it functions as a phrasal verb.

Catchup is one word and is mainly recognized as a less common spelling of ketchup.

The noun related to catching up is a separate matter. Major dictionaries show it as a hyphenated form. That noun can describe a meeting to exchange news or the process of reaching the same level. (Oxford Learner’s Dictionaries)

This means you should not assume that English always keeps catch and up together just because the words are pronounced as a unit.

Meaning

Catch up means to reach a person or level. It can also mean to become current with information or unfinished work.

Catchup usually refers to the condiment spelling.

That difference is much larger than a simple spelling variation.

Grammar

Catch up functions as a verb phrase.

She needs to catch up.

They caught up with us.

I am catching up on my assignments.

The word catch changes tense while up stays unchanged.

She catches up.

Rose caught up.

She is catching up.

She will catch up.

That behavior gives you a useful diagnostic. If the expression needs a verb tense, you are dealing with the phrasal verb catch up.

Pronunciation

The spoken forms can sound very similar. That is one reason learners make the mistake.

Cambridge gives the pronunciation of catch up with the main stress on catch. The noun catchup used for the sauce has a similar sound. (Cambridge Dictionary)

The spelling therefore carries more grammatical information than the sound does.

Writing Style

In everyday writing, catch up is standard.

It works naturally in texts, emails, school assignments, business communication, journalism, and general prose.

The one word catchup should not replace it.

The noun related to catching up is more specialized because noun compounds can develop different spelling conventions. That is why you may encounter catch up as a verb and a hyphenated noun in the same dictionary family.

Professional Writing

Professional editors generally care about the grammatical function first.

If the phrase is doing the job of a verb, write catch up.

If the expression is a noun, consult the applicable style guide and dictionary because compound noun spelling can vary.

That distinction is more reliable than trying to memorize every possible form as a fixed spelling rule.

Why People Confuse Between Catchup vs Catch Up

Similar Pronunciation

Speech is probably the biggest reason.

When people say catch up quickly, the boundary between the two words becomes less noticeable. Natural speech compresses sounds. The listener hears one smooth unit even though the writer needs to represent two words.

English has many phrasal verbs that behave this way.

Give up.

Pick up.

Find out.

Log in.

Call back.

Catch up belongs to the same broad pattern.

Typing Habits

Fast typing can turn two short words into one.

This is especially easy when a person writes by sound rather than by visual memory. Since catchup looks plausible, the mistake can slip past a quick reread.

Autocorrect

Autocorrect can make things worse because software does not always understand the grammatical role of a phrase. A keyboard may recognize catchup as a word because dictionaries contain it for the condiment.

That does not mean it is correct in your sentence.

Internet Myths

Online writing often spreads informal spellings. Once a misspelling appears often enough, readers can start treating it as an accepted alternative.

Frequency alone does not establish standard usage.

A word can appear thousands of times online and still be an error in edited English.

Learning Mistakes

English learners often memorize vocabulary by sound. That approach works well for some words but becomes risky with phrasal verbs.

If you learn catch up as one spoken chunk, you may naturally want to write it as one word.

The better approach is to learn the phrase together with its grammar.

Grammar Rules For Catchup vs Catch Up You Should Know

The key rule is functional rather than visual.

Catch up is a phrasal verb when it expresses the action of reaching or becoming current.

That means the verb catch carries tense.

Present tense.

I catch up.

Past tense.

I caught up.

Present progressive.

I am catching up.

Present perfect.

I have caught up.

Future.

I will catch up.

Notice that up never changes.

This is one of the easiest ways to recognize the phrase.

Catch Up With A Person

Use this structure when someone is being reached.

Subject + catch up + with + person.

I caught up with Maria after class.

We need to catch up with the rest of the group.

The runner finally caught up with the leader.

Catch Up On A Task

Use this structure when missed work or information is involved.

Subject + catch up + on + task.

I need to catch up on my emails.

She is catching up on her homework.

We spent the morning catching up on paperwork.

Catch Up With A Topic Or Information

You can also use catch up with when the meaning involves becoming informed.

I need to catch up with the latest developments.

He used the train ride to catch up with the news.

Cambridge documents catch up with something as a way to describe finding out recent information. (Cambridge Dictionary)

Formal Versus Informal Writing

Catch up is not limited to casual conversation. It is a standard phrasal verb and appears in professional and academic contexts when the meaning fits.

However, some formal documents may prefer a more specific expression.

Instead of saying researchers need to catch up on missed data collection, a technical report might say researchers need to complete the outstanding data collection.

That does not make catch up incorrect. It simply shows how register affects word choice.

A good writer does not avoid common phrasal verbs just to sound formal. The goal is precision.

Sentence Examples For Catchup Or Catch up That Sound Natural

The best way to remember this distinction is to see the words working in real sentences.

Examples With Catch Up

1. I need to catch up on my emails before the meeting.
2. She walked faster so she could catch up with her friends.
3. We stayed late to catch up on the work we missed.
4. I called Jake last night so we could catch up.
5. The team is trying to catch up with its competitors.
6. After missing two classes, Maya worked hard to catch up.
7. Let’s grab coffee tomorrow and catch up.
8. I spent Saturday catching up on my reading.
9. The younger runner managed to catch up with the leader.
10. I need to catch up on the latest news before I write the report.

Each example uses catch up as a verb phrase. The two words stay separate.

Examples With Catchup

The one word form is much less common in modern general writing because it is mainly an alternative spelling of ketchup.

1. The diner served catchup with every burger.
2. The old recipe calls for catchup and mustard.
3. The label used the spelling catchup instead of ketchup.
4. She found an old cookbook that used catchup.
5. The historical menu listed catchup as a condiment.
6. The bottle was labeled catchup.
7. The recipe mentioned catchup as a tomato sauce.
8. The restaurant offered catchup with the fries.
9. The cookbook used several older spellings including catchup.
10. Most modern readers would expect ketchup rather than catchup.

These examples are useful mainly because they show how unusual the one word form is for modern American readers. Merriam Webster identifies catchup as a less common spelling of ketchup. (Merriam-Webster)

Common Writing Mistakes For Catchup vs Catch Up and How to Avoid Them

Mistake One

I need to catchup on my work.

Correct it to:

I need to catch up on my work.

The verb phrase requires two words.

Mistake Two

We should catchup before the meeting.

Correct it to:

We should catch up before the meeting.

Again, the expression is functioning as a verb.

Mistake Three

She is trying to catchup with the class.

Correct it to:

She is trying to catch up with the class.

The meaning is reaching the same level. The verb remains two words.

Mistake Four

I have to catchup on the news.

Correct it to:

I have to catch up on the news.

The phrase means becoming informed.

Mistake Five

We had a catchup yesterday.

This sentence needs more attention because the writer is trying to use a noun.

The noun for a meeting where people exchange recent news is normally written in a hyphenated form by major dictionaries. Cambridge labels it an informal noun and gives examples involving meetings or conversations. Oxford also lists the noun for a meeting and for the process of reaching the same level. (Oxford Learner’s Dictionaries)

The practical lesson is important. Do not treat catchup as the universal spelling for every grammatical use of catch up.

Proofreading Tip

When you see catchup in your draft, stop and ask one question.

Am I talking about a condiment or am I describing the action of becoming current or reaching someone?

If the answer is the action, separate the words.

This simple test catches most errors immediately.

Catchup vs Catch Up Pronunciation Made Simple

Catch up is pronounced as a compact two syllable phrase.

The common pronunciation is approximately:

/kætʃ ʌp/

Cambridge gives this pronunciation for catchup as the sauce and a closely matching pronunciation for the phrasal verb. Oxford also lists the noun pronunciation as /ˈkætʃ ʌp/ and notes an alternate vowel in some British usage. (Oxford Learner’s Dictionaries)

Syllable Breakdown

Think of it as two spoken parts.

catch

up

The main stress falls naturally on catch.

Common Pronunciation Mistake

Some learners try to pronounce catchup as a single unusual word because they see it written together.

That is unnecessary for the verb.

Say catch and up as two connected words. In natural conversation they may run together. That does not change the spelling.

Easy Pronunciation Tip

Say this sentence slowly.

I need to catch up.

Then say it naturally.

I need to catch up.

The sounds connect smoothly. The spelling still keeps catch and up separate.

This is a useful reminder that pronunciation and spelling do not always map perfectly onto each other.

Word History and Origin For Catchup vs Catch Up

The history becomes especially interesting because the two forms come from different paths.

The phrasal verb catch up has a long history. Etymological records trace catch as a verb to Middle English and earlier French and Latin roots connected with taking or seizing. The expression catch up developed over time. The sense of reaching the same point or overtaking someone is recorded by the nineteenth century. (Etymology Online)

The noun catch up related to the idea of overtaking or reaching a rival developed much later. Etymological evidence dates that noun sense to the twentieth century and connects it with figurative use in American football. (Etymology Online)

The history of catchup is entirely different.

Catchup is an old spelling associated with ketchup. Etymological sources record early forms of the condiment word using several spellings. The history ultimately leads into words connected with Asian fish sauces and related terms. The modern tomato condiment developed later. (Etymology Online)

That means the two expressions may look related on the page, but their histories do not make them interchangeable.

Usage Of Catchup vs Catch Up Across English Speaking Countries

American English

American English uses catch up very commonly as a phrasal verb.

I need to catch up on work.

I will catch up with you later.

Let’s catch up soon.

American English also uses the noun catch up in some contexts. Cambridge identifies the noun referring to the process of reaching the same level as mainly US in one of its entries. (Cambridge Dictionary)

For general American writing, the verb rule is simple. Keep catch up as two words.

British English

British English also uses catch up as the standard phrasal verb.

The noun can refer to a meeting or conversation. Cambridge labels this use as UK in its dictionary entry. British English also has some structures that differ from American usage. For example, British English can use catch somebody up where American English more often uses catch up with somebody. (Oxford Learner’s Dictionaries)

The core spelling of the phrasal verb does not change.

Canadian English

Canadian English generally follows the same broad spelling pattern as American and British English for the verb.

Use catch up.

Regional differences can appear in vocabulary preferences and style. They do not turn the verb into catchup.

Australian English

Australian English also uses catch up as a phrasal verb.

The same basic grammar applies.

I need to catch up on my work.

She caught up with her friends.

They are catching up after the break.

As with other major English varieties, context determines the grammatical form.

The Important Regional Point

Do not assume that a regional variety makes catchup acceptable as the verb.

The major dictionaries consulted for this article consistently support catch up as the phrasal verb. (Oxford Learner’s Dictionaries)

Catchup vs Catch Up Real World Usage

Daily Conversation

Catch up is extremely natural in everyday speech.

I need to catch up with Sarah.

Let’s catch up this weekend.

I have a lot of shows to catch up on.

These sentences sound normal because catch up is an established part of everyday English.

School Writing

Students commonly use catch up when discussing missed work.

I need to catch up on my reading.

She worked after school to catch up with the class.

Teachers may also use it when talking about progress.

If you missed the lesson, review the material so you can catch up.

Business Communication

Catch up appears frequently in workplace communication.

I need some time to catch up on email.

Let’s catch up tomorrow afternoon.

The company is trying to catch up with competitors.

In business writing, the phrase is perfectly acceptable when the tone is appropriate.

Academic Writing

Academic writers can use catch up when the phrase is precise.

Students who miss several classes may need additional time to catch up.

However, highly technical academic prose may choose more specific wording when precision matters.

That is a matter of style rather than grammatical correctness.

Books

Catch up appears naturally in dialogue and narrative writing.

The character may catch up with another person physically. A character may also catch up on news or unfinished work.

Journalism

Journalists often use catch up when describing competition or progress.

A company may be trying to catch up with an industry leader.

A team may be trying to catch up after a slow start.

Online Writing

Catch up is common in blogs, newsletters, websites, and digital communication.

You may see phrases such as catch up on the latest updates or catch up with the newest episode.

Social Media

Social media makes the conversational meaning especially common.

I need to catch up on your posts.

Finally catching up after a busy week.

Let’s catch up soon.

The casual tone fits the expression naturally.

Catchup vs Catch Up Similar Words and Frequently Confused Terms

English has several expressions that can cause similar confusion.

Catch Up And Keep Up

Catch up means reaching a level you are currently behind.

Keep up means maintaining the same level or pace.

I need to catch up with the class.

I can keep up with the class now.

The first sentence describes closing a gap. The second describes avoiding a gap.

Catch Up And Get Up

Catch up and get up sound somewhat similar when spoken quickly but have completely different meanings.

Get up means rise from a seated or lying position.

I get up at seven.

Catch up means reach a person or become current.

I need to catch up on work.

Catch Up And Catch On

Catch on means understand something or become aware of it.

It took me a while to catch on.

Catch up means reach the same point or become current.

I need to catch up on the material.

Catch Up And Make Up

Make up can mean compensate for something missed.

I need to make up the class I missed.

Catch up can mean reach the same level after falling behind.

I need to catch up with the rest of the class.

The meanings can overlap in some situations but the phrases are not interchangeable in every sentence.

Catch Up And Follow Up

Follow up means take additional action after an earlier event or communication.

I will follow up with the client tomorrow.

Catch up means become current or exchange recent news.

I will catch up with the client tomorrow.

The first sentence suggests additional action. The second suggests a conversation or getting current.

Professional Editor’s Advice About Catchup vs Catch Up

A skilled editor does not treat spelling as a purely visual problem. The editor first identifies what the word is doing in the sentence.

That approach is especially useful with catch up.

If the expression tells us what someone is doing, it is probably the phrasal verb.

She needs to catch up.

If it tells us what someone is doing with a task or information, the same phrasal verb applies.

She needs to catch up on the report.

If it describes reaching another person or level, it is still the same phrasal verb.

She needs to catch up with the group.

This functional approach is stronger than memorizing a single spelling rule because it helps you handle new sentences.

Read The Whole Sentence

Do not proofread catchup in isolation.

Read the surrounding words.

If you see on or with after the expression, you are very likely dealing with the phrasal verb.

I need to catch up on my work.

We need to catch up with the team.

The grammar itself gives you a clue.

Check The Verb Tense

Look at the form of catch.

Caught up.

Catching up.

Catches up.

These forms prove that catch is functioning as a verb.

You would never write caughtup or catchingup in standard English.

The same grammatical logic tells you to keep catch up separate in the base form.

Watch For The Noun

The noun deserves special attention.

English often turns phrasal verbs into nouns. When that happens, spelling can change.

This is why dictionaries distinguish the verb catch up from the noun catch up that refers to a meeting or the process of reaching the same level. Oxford and Cambridge both document the noun. (Oxford Learner’s Dictionaries)

That noun is generally written in a hyphenated form in dictionary entries. The exact editorial treatment can depend on the style guide and dictionary you follow.

This is a good example of why English spelling cannot always be reduced to one mechanical rule.

Do Not Trust Autocorrect Blindly

If your editor accepts catchup, do not assume the sentence is correct.

Software checks spelling. It does not always understand your intended grammatical function.

A dictionary check is more useful when a word has multiple legitimate forms.

Use A Dictionary For Edge Cases

For ordinary sentences, your memory is enough.

For unusual noun uses, historical writing, specialized terminology, or publication style, consult a respected dictionary or style guide.

Oxford and Cambridge distinguish the verb and noun uses clearly. Merriam Webster also distinguishes the condiment spelling from the catch up family. (Oxford Learner’s Dictionaries)

That is the kind of source based approach professional editors use.

A Simple Memory Trick

Think of catch up as an action.

You catch up with people.

Use catch up on work.

You catch up on news.

You catch up to someone.

If you can put the phrase into a sentence describing something a person does, keep the two words separate.

For catchup, think of the condiment spelling.

A burger can have catchup.

A person cannot catchup with a friend in standard edited English.

There is one more useful memory trick.

Catch up moves. Catchup sits on food.

It is not a perfect linguistic rule. It is simply an easy way to remember the most important distinction.

Frequently Asked Questions About Catchup vs Catch Up

Is Catchup One Word Or Two

As a verb, the correct form is catch up and it has two words. Catchup as one word is recognized as a less common spelling of ketchup. Major dictionaries also recognize a noun related to catching up that is normally written as a hyphenated form. (Merriam-Webster)

Is Catchup Grammatically Correct

It can be correct in a very specific context when it means the condiment spelling of ketchup. It is not the standard verb spelling for reaching someone or becoming current with work or information. For those meanings, use catch up. (Cambridge Dictionary)

Should I Write Catch Up Or Catchup

Write catch up when you mean reach someone, reach the same level, complete missed work, learn recent information, or talk with someone to exchange news. Do not use catchup as the verb. If you mean the sauce, catchup is a recognized but uncommon spelling of ketchup. (Merriam-Webster)

Is Catch Up A Phrasal Verb

Yes. Catch up is a phrasal verb. It can mean reaching someone who is ahead, reaching the same level, completing something you missed, learning recent information, or exchanging news with someone. Oxford and Cambridge both classify catch up as a phrasal verb. (Oxford Learner’s Dictionaries)

Can I Say Catch Up With A Friend

Yes. This is a very common use. You can say I need to catch up with my friend or let’s catch up soon. The expression usually means talking with someone you know and exchanging news about what has happened since you last spoke. Cambridge specifically includes this conversational meaning. (Cambridge Dictionary)

Should I Say Catch Up On Work

Yes. Catch up on is the natural expression when you need to complete work that you did not finish earlier. For example, I need to catch up on my emails. Oxford lists this use for spending extra time doing something you did not do earlier. (Oxford Learner’s Dictionaries)

Is Catch Up Formal Or Informal

Catch up is standard English and works in both casual and professional contexts. The exact tone depends on the sentence. It is especially natural in conversation and workplace communication. In highly technical or formal academic writing, a more specific phrase may sometimes communicate the idea more precisely. That is a style choice rather than a grammar requirement.

What Is The Noun Form Of Catch Up

The noun can describe a meeting or conversation where people exchange recent news. It can also describe the process of reaching the same level as someone or something else. Major dictionaries generally show this noun in a hyphenated form. Cambridge identifies the meeting sense as UK and the reaching level sense as mainly US in its entries. (Cambridge Dictionary)

Why Do People Write Catchup

People often write catchup because the expression sounds like one unit in natural speech. Fast pronunciation can hide the boundary between catch and up. Autocorrect and online usage can also reinforce the spelling. Another source of confusion is that catchup is a real dictionary word when used as a less common spelling of ketchup. (Merriam-Webster)

Is Catchup The Same As Catch Up

No. The verb catch up means to reach someone or something, become current with missed work or information, or exchange recent news. Catchup as one word is mainly a less common spelling of ketchup. The noun related to catching up is a separate grammatical form and is normally written differently. (Merriam-Webster)

Final Verdict

The answer is straightforward once you separate grammar from sound.

Use catch up as the verb.

You catch up with a friend.

Use catch up with the latest news.

You catch up to someone who is ahead.

Do not write the verb as catchup.

The one word catchup is a recognized but uncommon spelling of ketchup. That meaning has a completely different history and function. Merriam Webster and Cambridge both identify it as a variant spelling of the condiment. (Merriam-Webster)

There is also a noun connected with catching up. It can describe a meeting where people exchange news or the process of reaching the same level. Major dictionaries generally write that noun in a hyphenated form. (Oxford Learner’s Dictionaries)

For everyday American English, you can keep the rule simple.

Catch up is the verb. Catchup is mainly the sauce spelling.

If you remember that catch up describes an action, you will avoid the most common mistake. The sound may run together when you speak, but the writing should keep the verb in two words.