The net amount of Social Security benefits a client received is shown in Box 5 of Form SSA-1099, the Social Security Benefit Statement. You report that Box 5 figure on line 6a of Form 1040 or Form 1040-SR, and the taxable portion on line 6b. Supplemental Security Income (SSI) is not a Social Security benefit, is not taxable, and does not appear on an SSA-1099. The taxable portion on line 6b is not a flat percentage; it is figured on a worksheet using the client's other income and filing status.

Where does the SSA-1099 go on the return?

Box 5 of the SSA-1099 is the net benefit, and it goes on line 6a of Form 1040 or 1040-SR. The taxable portion goes on line 6b. Line 6a carries the total benefit; line 6b carries only the part that is taxable for the year. If none of the benefits are taxable, line 6a still shows the total and line 6b is zero.

How do you know how much is taxable?

Whether any of the benefits are taxable is determined by a threshold test, not by judgment. Benefits may be taxable if the total of (1) one-half of the benefits, plus (2) all of the client's other income, including tax-exempt interest, is greater than the base amount for their filing status. The base amount is $25,000 for single, head of household, or qualifying surviving spouse; $32,000 for married filing jointly; and $0 for married filing separately if the client lived with their spouse at any time during the year. A married-filing-separately client who lived apart from their spouse for the entire year uses the $25,000 base amount.

When the test is met, the taxable amount itself is computed on the Social Security Benefits Worksheet in the Instructions for Form 1040 (and 1040-SR), or in IRS Publication 915. The worksheet output is what goes on line 6b. Run the worksheet rather than estimating the percentage.

What trips up SSA-1099 reporting in practice

A few things to confirm at intake and review. Tax-exempt interest counts in the threshold test even though it is not itself taxed, so a client with municipal bond income can have taxable benefits they did not expect. On a joint return, both spouses' income and benefits go into the same test, even if only one spouse received benefits. And SSI, which is not on an SSA-1099, sometimes gets confused with Social Security retirement or disability benefits; SSI is not taxable and is not reported here.

For a preparer, the SSA-1099 is a clean intake item: pull Box 5, drop it on line 6a, and let the worksheet decide line 6b. The judgment is not in the form, it is in making sure every income source that feeds the threshold test, including tax-exempt interest, was captured first. That capture step is where firms handling volume tend to standardize. If you are looking at how to handle return prep at scale, see how outsourcing tax prep fits on top of your existing process.

Sources: IRS, "Social Security income" (frequently asked questions, reviewed Sep. 5, 2025), irs.gov/faqs/social-security-income.