@dmertz Thank you for your answer containing useful information on 401(k) and traditional IRA. I am still not clear about the dates used for the calculation of taxable amount regarding Traditional IRA. In the case of distribution occurring on 15Feb2017 on Traditional IRA, I think the brokerage used the traditional IRA balance of 12/31/2016 to calculate the distribution amount according to IRS "Required Minimum Distribution Worksheet". However to calculate taxable amount for 2017 tax return I apply the balance of 12/31/2017 when using your method above which had an example of $190,000 2017 year-end balance? 12/31/2016 balance and 12/31/2017 balance can be very different while both balances are for the same distribution.
