How much of my social security retirement benefits check should I have withheld monthly?

[davelyon100]

still working.  Married filing jointly

[SweetieJean]

That depends upon upon your total taxable income and other factors.  You could instead increase your paycheck withholding and/or make periodic estimated tax payments.  Try this (for 2020, but should give a 2021 approximation):

Tax Calculator and Refund Estimator 2020-2021 | TurboTax® Official (intuit.com)

[davelyon100]

thanks.  Calculator is a great tool!  Good general answer.  Now specifically, what are the rules? 

[ToddL99]

There are no specific rules on how much to withhold from your Social Security.  

The amount you withhold from any source of income (wages, social security, pension, etc), depends on your overall income. Also, you can withhold more from one source of income (e.g. social security) to make up for withholding less (or nothing) from another source (e.g. pension). The objective is to have your total withholding (from all sources) closely match your total tax liability.

See IRS Tax Withholding Estimator