factor in (something)

Counting or adding numbers, time, money, etc. can be tricky in real-life situations. You have to make decisions about what things to include, or "factor in", and what things to leave out.

For example:

I thought I'd have plenty of time to get here, but I didn't really factor in the traffic.

When you were calculating the cost, did you also factor in taxes?

This phrase appears in these lessons: