Perhaps my case is different but the wife and I are both on social security and I am having to take the mandatory distributions from my 401k, and I have not paid any income tax since I retired.
It is not my calculation, I go to a tax preparer every year for them to run the numbers and it is always, no tax due.
If I may ask, are you paying taxes in your SS checks and are you paying taxes when you withdraw from your 401K? (Assuming it's a traditional / tax-deferred 401K and not a Roth 401K.) I'm basically asking if your tax liability is zero, or if you have a tax liability but the amount you pay in taxes throughout the year is enough to not force you to write a check in April.
The prior is preferrable and a statement of no taxes on seniors in your situation. The latter is matter of preferring one process of paying taxes over another (pay taxes throughout the year, or one time in April).