Provisional income between $25,000 - $34,000 for single filers, $32,000 - $44,000 for joint filers, up to 50% of Social Security benefits will be taxable. Provisional income above $34,000 for single filers or above $44,000 for joint filers, up to 85% of Social Security benefits will be taxable.

Social Security is based on lifetime earnings. The first step in calculating retired-worker benefits is adjusting (or indexing) earnings to account for changes in general wage levels over time. Doing so ensures retirement benefits reflect any increase in living standards realized while the worker was employed.

Not all Social Security income is taxable. Review total income yearly to know if you must file. A small change could mean a big tax surprise.