dmertz stated: "To complete the calculations on Form 8606, TurboTax has to assume something for the missing amount needed on line 6."
When the RMD amounts (gross and taxable) and taxes paid on the RMD's have been entered into TT, why not assume the tax due is based on the taxable amount at that point and not wait to determine tax on the RMD until later. That would initially show the higher amount of taxes due or lower amount of refund. Then when TT asks for the total basis amount of the IRA and market value at end of reporting tax year, the adjustment made would not be a shock to the taxpayer. For example, my total basis is less the a few percent of the market value. Using the example of the OP where tax due increased by $1000, calculating taxes on RMDs reported would show amount due would be $1030 if total basis is 3% of the market value. The taxes due would then drop to $1000 when the basis and market value have been entered. End result the same but less shock to the TT using taxpayer.
