What you can do in that case is just make your IRA deduction as normal, then call your broker and recharacterize the non-deductible portion to Roth once your numbers are in. You have until your tax filing deadline, with an extension if you filed for that to do this. So you don't have to guess correctly about whether you can deduct or not.
Or you could wait until your tax documents are all in and make your decision early next year - you have until your tax filing deadline (no extension) to fund an IRA for a given tax year, so for 2019 IRA contributions, you don't have to make the contribution until April 15th 2020.