Social Security and taxes: when benefits become taxable

A common assumption is that Social Security is tax-free. It often isn’t — depending on total income, up to 85% of the benefit can be subject to federal income tax, a detail that surprises a lot of new retirees the first time they file.

The formula: combined income

Whether — and how much — of a benefit is taxable depends on “combined income”: adjusted gross income, plus nontaxable interest, plus half of Social Security benefits. The thresholds (which haven’t been adjusted for inflation since they were introduced, meaning more retirees cross them every year as incomes rise) determine the taxable portion:

• Below the lower threshold: benefits aren’t taxed
• Between the lower and upper threshold: up to 50% of benefits may be taxable
• Above the upper threshold: up to 85% of benefits may be taxable

The SSA’s guidance on benefits and taxes has the current thresholds and a worksheet for estimating the taxable portion. Critically, this is “up to” 85% — it’s never the case that more than 85% of a benefit is taxed, even at very high income levels.

Why withdrawal timing affects this

Because the formula counts other income, the order and timing of retirement account withdrawals directly affects how much of a Social Security benefit gets taxed in a given year. A large traditional IRA withdrawal in the same year as claiming Social Security can push combined income into the 85%-taxable range, where a smaller or differently-timed withdrawal might not. This is one of the more concrete reasons withdrawal sequencing (covered in Withdrawal strategy basics) and Social Security claiming decisions tend to get planned together rather than separately.

State taxes are a separate question

The federal rules above apply regardless of where you live. Some states additionally tax Social Security benefits at the state level, while many don’t — worth checking your specific state’s treatment as part of any broader retirement tax planning, separate from the federal calculation. The IRS’s FAQ on Social Security income covers the federal rules specifically.

Where to get personalized guidance

Because the taxable portion depends on the interaction of multiple income sources and account types, a tax professional or financial planner can model how a specific withdrawal and claiming plan affects taxes on Social Security in a given year — often a more useful exercise than trying to estimate it from the worksheet alone.

Related reading: Withdrawal strategy basics and How your Social Security benefit is calculated.