I wrote this as (hopefully) a helpful guide for those confused or unsure of when to say the word "then" vs when to use the word "than".
The word "than" is used to compare.
Anne is prettier than Sue.
(Anne is being compared to Sue.)
It is farther than you think.
(The actual distance is being compared to the distance you're thinking.)
Will it take less than five minutes?
(The actual time it will take is being compared to five minutes.)
I would rather do it today than tomorrow.
(Today is being compared to tomorrow.)
The word "then" is a bit trickier as it can be used in different ways with various meanings. The trick is if you can substitute any of the following words or phrases for it, "then" is the right word to use:
at that time
also / in addition / besides
in that case / therefore
on the other hand / at the same time
To give some examples…
The term "then" can be used to signify a point in time (answers the question "when?"):
I'll see you then.
Call me tomorrow, I'll answer your questions then.
I decided to do it right then.
"Then" can be used when talking about a sequence of events or order of things in a sequence:
Put the eggs in first, then put in the flour.
You can have a snack, then go to bed.
One, then two, then three…
The word "then" can be used to mean "also" or "in addition":
The cost of the refrigerator is $800, then there's the warranty costs too.
The icemaker doesn't work, and then there's the issue with the missing shelves.
"Then" can also be used to say "in that case" (often "if" will be used in the sentence):
If you think it might hurt her, then you shouldn't tell her.
I want to dance.
Then let's dance!
The word "then" can also be used to mean "at the same time" or "on the other hand" (often preceded by "but"):
The purple one is great, but then so is the red one.
I don't like the dark, but then I love going out at night.
Examples showing both Than and Then
That was then rather than now.
Then I told him I would be more than happy to help.
Of course, if you understand "than" is always used to compare (greater than, less than, heavier than, smaller than, earlier than, better than, quicker than), then you won't have any problem. Use "then" for all other cases.