My wife and I are both retired drawing SS and were both working last year. My wife now quit her job.How can we determine quarterly estimated tax payments for next year?

Read this info

https://turbotax.intuit.com/tax-tips/small-business-taxes/estimated-taxes-how-to-determine-what-to-pay-and-when/L3OPIbJNw

Are you self-employed or working for an employer?  If you are working for an employer, you would not need to make estimated tax payments, instead you would fill out a new W4 to have them increase your withholdings or you could contact Social Security and have them withhold taxes as well.

If you are self-employed, you would calculate your estimated quarterly taxes by taking your self-employment income for the quarter and multiplying that by 15.3%  Then adding either 50% or 85% of your social security to it based on the chart below, adding that to your self-employment income and any other income to arrive at your total income then using your tax rate multiplied by your total income divided by 4. 

You can also use TaxCaster or Quickbooks Self-Employed to calculate your estimated taxes. 

If you fall into the following, 85% of your social security is taxable income

• Single with income above $34,000
• Married Filing Jointly with income above $44,000
• Married Filing Separate regardless of income

If you fall into the following, 50% of your social security is taxable income

• Single with combined income between $25,000-$34,000
• Married Filing Jointly with combined income between $32,000 and $44,000

Your combined income is calculated by adding your

• AGI plus
• Nontaxable Interest plus
• 1/2 of your social security Benefits

Social Security Benefits Taxes