@George4Tacks "Must be a lot of SS income" -- or, more likely, there are Schedule B and W-2 income.  This is high school algebra, the formula is the same as what programs compute when there is an IRA deduction along with SS income.  Most of us have replaced high school algebra with more pleasant memories, so it is either "trial and error," or do a Google search for a formula that no doubt someone has already discovered.  

If the NOL carryover is $10k, why not just input $8K in the first place and find out how much SS is taxable with that amount?  Then figure out what, if anything, needs to be overridden from there.