OK I'll answer my own question as I just researched it. From the IRS:
"A quick way to find out if any of your benefits may be taxable is to add one-half of your Social Security benefits to all your other income, including any tax-exempt interest. Next, compare this total to the base amounts below. If your total is more than the base amount for your filing status, then some of your benefits may be taxable. The three base amounts are:
•$25,000 - for single, head of household, qualifying widow or widower with a dependent child or married individuals filing separately who did not live with their spouse at any time during the year
•$32,000 - for married couples filing jointly
•$0 - for married persons filing separately who lived together at any time during the year"
You must add 1/2 of your social security benefits to your other income, so in my previous illustration of a couple drawing $34,800 in social security benefits, half of this amount is $17,400 - $32,000 = $14,600. So in this illustration the couple could have another $14,600 in additional income through wages, pension, etc. and still not have to pay federal income tax.
https://www.irs.gov/uac/newsroom/are-your-social-security-benefits-taxable
Chip
