when adding lines 7 thru 21 and there is a neg # is it substracted on f1040?

For what purpose?

What do those instructions say?

Line 14 is a business loss, and as a result it result in an NOL. That is, if your AGI is negative on account of line 14, then you can carry the loss back two years, or forward 10 years. I might have these two numbers incorrect. To carryback means that you file an amended return for the earliest previous year subtracting the the NOL. As a result you get a refund, but I don't think they pay interest on it. If in that year you still have a loss, then you carryforward the negative amount to the next earliest year. You also need to fill out a form

You say "can carry". Does the taxpayer get the choice? (E.g. maybe two years ago he was in a low bracket, and last year in a high one, so he's better off carrying it back only one year. Or maybe he expects to be in a higher bracket next year, so carrying it forward (only) is better.)

Seth

You can elect not to carry back the loss [172(b)(3)]. The choice is (generally) irrevocable. See Publication 536 for details.