Free Social Security Taxability Calculator
While researching an article on the impact of the recent One Big Beautiful Bill Act (OBBBA) I stumbled upon a very useful, free Social Security Taxability calculator. The calculator is a downloadable Excel spreadsheet. I found it while viewing a YouTube video presented by The Retirement Nerds. The video did a nice job of explaining some of the provisions of the tax bill, especially the new $6,000 bonus senior deduction. The presenter used the calculator to demonstrate the interaction between income, SS taxability, and how the new deduction comes into play.
I wasn’t familiar with this site or the presenter so I did a bit of research and it seemed legitimate so I downloaded it from this site. I’ve played around with it a number of times and I’m pretty impressed. It is not a complete tax return calculator, but it does a few things well, and provides some useful information for what-if studies. It has been updated for to include the 2025 tax law changes, including the new senior deduction.
In general, you input your “base case” which is your AGI, tax-exempt income, the amount of your SS benefits, and any applicable Schedule 1 adjustments (there is a tab that describes them). The tool calculates the percent, and amount, of your SS benefit that is taxable. It shows the details of that calculation – one of the more complex calculations in the tax code. It also determines your standard deduction, your new senior deduction (if any), taxable income, estimated tax, effective tax rate, and marginal tax bracket. It includes a nice table, and graphic, that shows how much income “headroom” you have until you reach the next tax bracket.
One of the more interesting features is a large table entitled “Incremental scenarios adding more non-Social Security Income”. This table provides 25 rows to investigate the impact of additional income on your tax calculation. You input a dollar amount in the first row, and it increments each row by that amount. For example, if you input $1,000 in the first row, the succeeding rows will be $2,000, $3,000 and so on up to $25,000. The columns in the table update some of the previous tax calculations for the new income amount, with the end result being the revised taxable income. It has a column that clearly shows how, in certain situations, an additional $1 of income can pull additional SS benefits into the taxable category, and how the effective marginal tax rate can be greater than the marginal tax bracket.
There is also nice graphic to the far right that shows a summary of the base case, including how the calculated tax falls into the marginal tax brackets. Someone looking to understand how the taxable portion of your SS benefit is determined, and how additional amounts of income impact your overall tax situation, may find this useful. Roth Conversion studies would be another good use of the tool.
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