You must include the taxable part of a lump-sum (retroactive) payment of benefits received in the current year in your current year's income, even if the payment includes benefits for an earlier year.

Generally, you use your current year's income to figure the taxable part of the total benefits received in the current year. However, you may be able to figure the taxable part of a lump-sum payment for an earlier year separately, using your income for the earlier year. You can elect this method if it lowers the taxable portion of your benefits. Refer to Publication 915, Social Security and Equivalent Railroad Retirement Benefits, for a detailed explanation of the election and worksheets. Refer to Tax Topic 423, Social Security and Equivalent Railroad Retirement Benefits.

The amount of income tax, if any, that you must pay on the social security benefits you receive depends on the total amount of your income and benefits for the taxable year. If you are married and file a joint return, you must combine your incomes and your social security and equivalent tier 1 railroad retirement benefits when figuring the taxable portion of the benefits.

The taxable amount of the benefits is figured on a worksheet in the Form 1040 Instructions or Form 1040A Instructions book, or in Publication 915, Social Security and Equivalent Railroad Retirement Benefits. Refer to Publication 915, for base amounts and additional information regarding taxability and reporting requirements. Or, Tax Topic 423, Social Security and Equivalent Railroad Retirement Benefits, includes additional information regarding taxability and reporting requirements.