Use this calculator to estimate your self-employment taxes. Normally these taxes are withheld by your employer. However, if you are self-employed, operate a farm or are a church employee you may owe self-employment taxes. Please note that the self-employment tax is 12.4% for the Federal Insurance Contributions Act (FICA) portion and 2.9% for Medicare. The FICA portion funds Social Security, which provides benefits for retirees, the disabled, and children of deceased workers.