To calculate taxable Social Security income, compare total income plus one-half of the Social Security benefit amount to the applicable base. Income in excess of the base amount is taxable, according to the Social Security Administration. Benefits that are a sole source of income are usually not taxable.
As of 2015, the base amount is $25,000 for those filing single or head of household, for qualifying widows or widowers with dependents, or married individuals filing separately if they did not live with a spouse during the tax year. The base amount for married couples filing a joint return is $32,000. The base amount is $0 for married persons who lived together at any point during the year but who file separate returns, according to the IRS.
When income, including earned income, income from self-employment, Social Security benefits and interest income, exceeds the base level, benefits become taxable. Individuals with incomes from $25,000 to $34,000 may have to pay tax up to 50 percent on the benefits received, or up to 85 percent of the benefits received when income exceeds $34,000. Taxpayers filing joint returns with combined incomes from $32,000 to $44,000 may have to pay tax on up to 50 percent of benefits received, or tax on up to 85 percent of benefits received for combined incomes in excess of $44,000, according to the Social Security Administration.