Updated October 17, 2026. Quick answer: Line 6a is for your social security benefits and line 6b is the taxable part. The benefits come from Form SSA-1099, or Form RRB-1099 for railroad retirement benefits treated as social security. The instructions send most filers to the Social Security Benefits Worksheet to find the taxable amount, and lines 6c and 6d are boxes for two special situations.
IRS worksheets read line by line: Social Security Lump-Sum Worksheet 2, Social Security Lump-Sum Worksheet 3 and Social Security Lump-Sum Election Worksheet 4.
More IRS forms and schedules for individual filers, read line by line: Schedule R instructions and Schedule R Part III credit calculation.
Related reading on this site: IRS Publication 915.
Read box by box from the IRS form text: Form RRB-1099-R boxes 7 to 12.
IRS worksheets from the 2025 Form 1040 instructions, read line by line: Social Security Benefits Worksheet.
What goes on line 6a and line 6b
The instructions start with the tax form that reports the benefits: “You should receive a Form SSA-1099 showing in box 3 the total social security benefits paid to you.” “Box 4 will show the amount of any benefits you repaid in 2025.” “If you received railroad retirement benefits treated as social security, you should receive a Form RRB-1099.”
The form captions are “Social security benefits” for line 6a and “Taxable amount” for line 6b. How to read the SSA form box by box is on the SSA-1099 page, and the other income lines are on Form 1040 line by line.
The worksheet that finds line 6b
The instructions answer the taxable question with a worksheet: “Use the Social Security Benefits Worksheet in these instructions to see if any of your benefits are taxable.” The worksheet’s first line is “Enter the total amount from box 5 of all your Forms SSA-1099 and RRB-1099.” It continues “Also enter this amount on Form 1040 or 1040-SR, line 6a”. The introductory paragraph names boxes 3 and 4, and the worksheet names box 5, so compare each against the Form SSA-1099 you actually received.
The worksheet pulls in your other income lines. Line 3 reads “Combine the amounts from Form 1040 or 1040-SR, lines 1z, 2b, 3b, 4b, 5b, 7a, and 8”. That is why it is easiest to fill in lines 1z through 8 first. Those lines are explained on the line 1z page, the lines 2a and 2b page, the lines 3a and 3b page, the lines 4a and 4b page, the lines 5a and 5b page and the line 7 page.
The answer lands on line 6b. In the worksheet’s words, “Taxable social security benefits. Enter the smaller of line 16 or line 17.” and, if the result is none, “None of your social security benefits are taxable. Enter -0- on Form 1040 or 1040-SR, line 6b.”
When not to use that worksheet
The instructions list three exceptions, introduced by “Do not use the Social Security Benefits Worksheet in these instructions if any of the following applies.”
First: “You made contributions to a traditional IRA for 2025 and you or your spouse were covered by a retirement plan at work or through self-employment.” “Instead, use the worksheets in Pub. 590-A to see if any of your social security benefits are taxable and to figure your IRA deduction.”
Second: “You repaid any benefits in 2025 and your total repayments (box 4) were more than your total benefits for 2025 (box 3).” “None of your benefits are taxable for 2025.” Third: “You file Form 2555, 4563, or 8815, or you exclude” certain employer-provided adoption benefits or “income from sources within Puerto Rico.” “Instead, use the worksheet in Pub. 915.”
Line 6c: the lump-sum election
The form caption is “If you elect to use the lump-sum election method, check here”. The instructions say “Check the box on line 6c if you elect to use the lump-sum election method for your benefits.” They describe when it matters: If your benefits are taxable for 2025 and include a lump-sum benefit payment for an earlier year, the instructions say “you may be able to reduce the taxable amount” with the lump-sum election. “See Lump-Sum Election in Pub. 915 for details.”
Line 6d: married filing separately and lived apart
The form caption is “If you are married filing separately and lived apart from your spouse the entire year”. The instructions give the rule: “If you are married filing separately and you lived apart from your spouse for all of 2025, check the box on line 6d.” The consequence they state is “If you don’t check the box on line 6d, you may get a math error notice from the IRS.”
The same check appears at the top of the worksheet. The worksheet also has a separate path for a different case: “Married filing separately and you lived with your spouse at any time in 2025, skip lines 8 through 15”. So the answer to whether you lived apart for all of the year changes which lines of the worksheet you fill in.
Where the number comes from
Line 6a comes from Form SSA-1099 or Form RRB-1099 and the worksheet’s first line, and line 6b comes from the last step of the worksheet (or from the publication named in an exception). For a retired worker looking at how benefits and other income interact, see the social security tax torpedo page.
Where it goes next
Line 6b goes into the income total. The form’s line 9 reads “Add lines 1z, 2b, 3b, 4b, 5b, 6b, 7a, and 8. This is your total income”. Line 6a is not in that list; line 6b is. The totals are explained on the lines 9, 10 and 11 page, and the form itself is on the Form 1040 page.
Edition and line numbers
This page reads the 2025 Form 1040 and its 2025 instructions. Those are the files irs.gov was serving as the current ones on 2026-10-17, and they are for the tax year 2025 return, filed in 2026. Check the tax year printed on the form in front of you and use the line numbers on that year’s form. For the 2025 edition, the instructions state: “The lines on Forms 1040 and 1040-SR are the same.” The 2025 form has lines 6a, 6b, 6c and 6d in the income section, and the worksheet cited here is the one printed in the 2025 instructions.
Common mistakes
- Using the instructions’ worksheet when an exception applies. The instructions say “Do not use the Social Security Benefits Worksheet in these instructions if any of the following applies.”
- Skipping line 6d when you are married filing separately and lived apart all year. The instructions warn “you may get a math error notice from the IRS”.
- Putting the taxable amount on line 6a. The worksheet says to enter the total “Also enter this amount on Form 1040 or 1040-SR, line 6a” there, and the taxable amount goes on line 6b.
Related: SSA-1099 decoded, Social security tax torpedo, Form 1040, and Schedule 1 Form 1040.
Sources
- Instructions for Form 1040 and Form 1040-SR (2025): https://www.irs.gov/pub/irs-pdf/i1040gi.pdf
- Form 1040, U.S. Individual Income Tax Return (2025): https://www.irs.gov/pub/irs-pdf/f1040.pdf
Read from the IRS documents linked above on October 17, 2026. General information, not tax advice. Your own facts decide the outcome, and a preparer, the account provider or the IRS is the right place to confirm anything consequential.