Looking for some help. I'm doing our taxes on Tax Act and when I get to the 401K part I have some questions.

What counts as a deductible contribution? Is that just your contribution for the year? Or only your gain for the year?

Let's say my husbands year end 401k statement says his annual contributions this year were $10,000. But his gain was only $5000. Which do you enter?

Are either of those even considered deductible contributions? I guess my question is, how do you know if something is considered a deductible or not.