How Is a Retention Bonus Taxed?

Retention bonus tax for employees is considered on a case-by-case basis, according to Elaine Varelas for the Boston Globe. A retention bonus is considered for tax in the year that it is paid, and it is taxed at the employee's usual tax rate. Retention bonuses are treated like any other end-of-year bonus. The FICA rules still apply to retention bonuses, so they are liable for Social Security and Medicare contributions.