FICA is the acronym for Federal Insurance Contributions Act and is calculated at 6.2% of gross wages minus pre-tax deductions such as family medical and dental premiums up to a limit of $87,900 for 2004. The tax is withheld for contributions towards your Social Security account for your retirement benefits through the Social Security Administration. MEDI is the Medicare tax withheld for contributions to the social insurance system better known as Medicare insurance. It is calculated at 1.45% of gross wages minus pre-tax deductions such as family medical and dental premiums. There is no limit on wages on which the tax is calculated.