Then vs. Than
This is an extremely common and popular grammatical error.
THEN has an element of TIME attached to it. For example, it can mean “next Wednesday” or “next week”.
Example: We will finish the homework assignment, then we will go to the ice skating rink.
THAN refers to a comparison. A way to remember this rule is that the “A.” in THAN is shared in the word COMPARISON.
Example: I like this shirt more than that one.