Than is used to draw a comparison between two or more items, while then is used in relation to time and the order in which events occur. (For example: Julie had been taller than her little brother at the start of the year, but then Corey grew over the summer until he stood half an inch taller than his sister.)
Comparison chart
 | Than | Then |
|---|---|---|
| Meaning | Used in relation to time and the order in which events occur. | |
| Used As | An adverb, adjective, or a noun. | |
| Examples | She ended the call, then packed her bags. "Until then," she said. | |
| Idioms | Now and then, then and there. | |
| Etmology | From Old English. Used as a noun starting in the 1300s. Used as a conjunction, adjective, and adverb starting in the 1500s. No longer used as a conjunction starting in the 1700s, when "than" developed. |
When to Use "Than"
Than is used as a conjunction or preposition to compare items and draw attention to differences. It is found in numerous idiomatic expressions (e.g., easier said than done, more than meets the eye, better safe than sorry).
"Than" Examples
Than is used after comparative adjectives and adverbs:
- I ate more than he did.
- Their car was dirtier than Marco's and Paula's cars.
It can be used to show differences and choices. In these cases, it often follows words like anywhere, different, else, other, or otherwise.
- Drop me off anywhere other than there.
- His smile was different than she remembered.
Similar to the above, than can highlight rejected differences or exceptions. This usage can seem subtle, but the words sooner or rather will often feature in the sentence or could be imagined there.
- He would sooner fail the class than ask for her help. (He would rather fail than ask for help.)
When to Use "Then"
Then is an adverb that is used to communicate the time at which events occur. It can also communicate the order in which multiple events occur. One way to remember how to use then is to associate it with when.
Then can also be used as a noun or adjective, and is still in relation to time in these cases, but this usage is less common. As in the case of than, then is found in idioms (e.g., now and then, then and there), but far fewer.
"Then" Examples
- We were so worried then.
- She ended the call, then packed her bags.
- In the changing colors of the setting sun, his hair looked golden, then red, then brown.
- "Until then," she said.
- Chelsea Avery, the then CEO and President of the company, stood before the crowd with a smile.
Video Explaining the Differences
Mnemonic
An easy way to remember the difference is that then rhymes with when, so you use it to refer to timing.
It's 
Affect 
Who 
e.g. 
Lay 
Principal 
It's 
Affect 
Who 
e.g. 
Lay 
Principal 
Comments: Than vs Then