Then and than are different words with different jobs. Then mainly relates to time and sequence, answering when or what happened next. Than is used for comparisons, showing difference between two things. Keeping the meaning in mind is the most reliable way to choose the correct word.

Then refers to time, order, or the next step in a process. Use then when you can replace it with at that time, next, or after that. It often connects events in a sequence and helps describe what happens in what order.

Than introduces the second part of a comparison. Use than when you are comparing two things and can rephrase the idea as compared with. It commonly appears after comparative adjectives and adverbs such as bigger, faster, and more.

Use then to talk about a moment in the past or future, or to show the next event in a timeline. It can appear at the beginning, middle, or end of a clause depending on emphasis. If the sentence is about when something happens, then is the correct choice.

Rule	Example
Use then for a specific time	Back then, we didn’t have smartphones.
Use then for the next step in order	Finish your work, then call me.
Use then meaning after that	We ate dinner, then we watched a movie.

Use than to link two sides of a comparison, especially after comparative forms like -er and more. It can compare people, objects, amounts, or actions. If the sentence answers which one is greater, smaller, faster, or more intense, than is the correct choice.

Rule	Example
Use than after comparative adjectives	This road is narrower than the highway.
Use than after comparative adverbs	She runs faster than I do.
Use than with more or less	I have less time than yesterday.

Then and than appear in predictable sentence patterns. Recognizing these patterns helps you choose quickly while reading and writing. Then often follows an instruction or marks a next action, while than follows a comparative word or phrase.

Word/Phrase	Definition	Example
if… then…	result that follows a condition	If it rains, then we’ll stay inside.
now and then	occasionally	I go hiking now and then.
more… than…	comparison of degree	It’s more complicated than it looks.
rather… than…	preference between two options	I’d rather walk than drive.

Then usually acts as an adverb that modifies when or in what order something happens. Than is typically a conjunction or preposition that introduces what you compare something to. Thinking about the role in the sentence can confirm the correct choice.

Rule	Example
Then functions as a time or sequence adverb	We’ll meet at six and eat then.
Than introduces the comparison target	The meeting was longer than expected.
Then can connect two actions in one plan	Check the address, then send the package.

When you are unsure, replace the word with a short synonym to test the meaning. If next or after that fits, use then. If compared with fits, use than. This substitution test works in most everyday sentences.

Rule	Example
Replace with next to check then	Read the email, then respond.
Replace with compared with to check than	This option is cheaper than the other one.
If both seem possible, focus on time vs comparison	Is it about when, or about which is more.

A simple memory aid is to connect the spelling to the meaning. Then contains e like event and time sequence, while than contains a like compare. This is not a grammar rule, but it can help you proofread quickly.

Rule	Example
Then has e, think event order	First we talk, then we decide.
Than has a, think compare a to b	A is larger than B.

Use then for time, order, and what happens next. Use than for comparisons and differences between two things. If you check whether the sentence is about when or about comparing, you can choose correctly every time.