When the after-tax (non-deductible) contributions were made to the Traditional IRA a 8606 form should have been filed that reports that to the IRS and would document the after tax contribution on lines 1,3 and 14.
When you enter the 1099-R Traditional IRA to Roth conversion, you will be asked if you had and tracked any non-deductible contributions, then you will be asked for the amount. You would use the amount form line 14 from the last 8606 form that was filed. You will also be asked for the year end total value of all Traditional IRA, SEP or SIMPLE accounts that you still have so the taxable/non-taxable portion can be prorated over the current conversion and the remaining value of all existing accounts - that calculation is dome on line 6-15 on a new 8606 form.
Note, that a 8606 form is only filed for year that you had a new non-deducible Traditional IRA contributions/distributions, Roth conversions or Roth distributions. For years that none of those occurred then the last filed 8606 is the current form to use.
Also note, you mentioned RMD. If you are 70 1/2 or older the RMD distribution must be completed before any distribution in addition to the RMD can be rolled over or converted to a Roth.
**Disclaimer: This post is for discussion purposes only and is NOT tax advice. The author takes no responsibility for the accuracy of any information in this post.**
