Also see:
Additional information:
You cannot amend returns for prior years. You must include the taxable part of a lump-sum (retroactive) payment of benefits received (reported to you on Form SSA-1099) in the current year in your current year's income, even if the payment includes benefits for an earlier year.
There are two ways to determine the amount of income to include:
To find out whether any of your benefits may be taxable, compare the base amount for your filing status with the total of:
The base amount for your filing status is shown next:
The taxable amount of the benefits can be figured on a worksheet in the Form 1040 Instructions or Publication 915, Social Security and Equivalent Railroad Retirement Benefits.