How can I determine the how much of a previously made nondeductible ira contribution should be deducted from the taxable portion of my RMD?

[Critter]

The program will compute that for you in the 1099-R entry section ... leave box 2a blank and follow the interview to enter the prior year unrecaptured non deductible contributions ... if you captured some in previous tax years look to the form 8606.