I think we’ve all been a little guilty of this one. You are writing a great article, a letter, or something and you misuse the words then or than. It’s pretty easy to do. So let me explain the difference, so you don’t flub again.
Then is an adverb. It is used for TIME. It can be used several ways to describe:
1 at that time, at the time in question
Example: I was living in New Jersey then.
2 after that, next, afterward
Example: She played the first then the second game.
3 in that case, therefore
Example: If you save your money, then you won’t have to worry about how you will pay your bills.
Than is typically used as a conjunction. It is used for comparisons.
1 introducing the second element in a comparison
Example: He was much bigger than his dad at that age.
2 used in expressions introducing an exception or contrast
Example: She claims not to own expensive jewelry other than her wedding ring.
When making a decision between than or then, than is used for comparisons. If it’s not a comparison, use then.
Resource I like: English Grammar For Dummies