When writing in English, it is essential to know about the different sentence types and how to use these accurately. One of the most common types of sentence is the compound sentence, which can be constructed quite easily by learning a simple formula.

compound sentence formula

The Compound Sentence Formula

A compound sentence is made up of two independent clauses, joined by a comma and a coordinating conjunction. Here is the basic formula:


To illustrate how this works, let’s look at an example:

Exams are boring,butthey are quite important.

As you can see, with this easy formula, writing a compound sentence is not difficult at all! However, if you want to understand completely then you should read on for more useful information.

More About Compound Sentences

Let’s talk a little more about compound sentences so that you can understand precisely what I mean by the above formula. A compound sentence is essentially a sentence comprised of two independent clauses. As such, to understand how they work, you need to know what an independent clause is.

What are Independent Clauses?

Independent clauses are clauses that contain three things:

  1. Subject
  2. Verb
  3. Complete thought

For example:

  • Susan drives to work.
  • The dog was sleeping on the porch.
  • Her car was stolen last night.

Each of these sentences contained a subject (Susan, the dog, her card) and a verb (drives, was sleeping, was stolen). They are also self-contained ideas because they have a complete meaning.

What are Coordinating Conjunctions?

The phrase “coordinating conjunction” might be unfamiliar, but don’t worry! I did not know what a coordinating conjunction was until I began working as an English teacher 15 years ago. It is not really important to know this term.

Basically, these are a group of words that can be used to link independent clauses in a compound sentence. The easiest way to remember them is through the acronym FANBOYS:

  • For
  • And
  • Nor
  • But
  • Or
  • Yet
  • So

Each of these can be used to show the relationship between the different parts of the sentence. For example, “but” shows contrast. We use “nor” for joining negative ideas.

Here are some examples:

  • She walks to work each day, for she is trying to lose weight.
  • The baby sleeps at night, and his mum can get some rest.
  • I don’t like peas, nor do I like celery.
  • We watch movies on Fridays, but she can’t make it this week.
  • I can offer you coffee, or I can offer you tea.
  • It was a scary movie, yet it was funny in places.
  • I’ll watch your stuff, so you can go to the bathroom.

Is the Comma Really Necessary?

You may have noticed in those example sentences above that the comma sometimes seems a bit out of place. It’s true. We often skip the comma in compound sentences, particularly when the two clauses are quite short. Commas are a guide to the reader to signal a break between two clauses and there are complex rules governing their use; however, sometimes we do omit them. I would advise you to include them for your exam wherever necessary, but don’t worry too much about it – comma use isn’t hugely important for your IELTS score.

Another Formula: Compound Sentences with Semi-Colons

The above compound sentence formula is the most important one, but there are actually two other compound sentence formulas that are much less common. I would say that 99% of compound sentences adhere to the first rule, but I want to add these two formulas just in case you are wondering about them.

compound sentences with semi-colons

Compound Sentence with Semi-Colon and Conjunctive Adverb

The second most common type of compound sentence includes a semi-colon and a conjunctive adverb. Its formula looks like this:


Conjunctive adverbs are words like “therefore,” “otherwise,” “however,” and “meanwhile.” These are pretty common and in most cases you would use them to start a new sentence, but sometimes you might use a semi-colon and comma to split the two independent clauses of a compound sentence. Here are some examples:

  • The man broke the law; therefore, he must face the consequences.
  • It was raining; however, we still went for a walk.

Compound Sentence with Semi-Colon (and not Conjunctive Adverb)

The second compound sentence formula is simply:


This is uncommon because often it just does not work. It can be confusing to link two independent clauses in this way unless the relationship between them is really clear and obvious. For example:

  • She came home early; her work was done for the day.
  • They took their positions; the race was about to begin.

Honestly, in these cases, we would most likely switch to a complex sentence and use “because” to show the relationship, but very occasionally it may be acceptable to use this formula.

A Video Guide to Sentence Types

If you are still wondering about sentence structure, you can check out this video that I made:

It is part of a 10-day IELTS writing course I designed to help people build their grammar skills. The course can be accessed for free here without any sign-up.