"Catch-up contributions" are supplemental tax-deferred employee contributions that employees age 50 or older can make to the Thrift Saving Plan (TSP) beyond the maximum amount they can contribute through regular contributions. To be eligible to make catch-up contributions, you must be: age 50 or older during the calendar year in which the catch-up contributions are made and contributing an amount that will cause you to reach the Internal Revenue Service (IRS) elective deferral limit ($19,500 in 2021) by the end of the calendar year. The maximum "catch-up contribution" in 2021 is $6,500.
If you entered a valid catch-up contribution amount, this amount will be included in the overall TSP balance for purposes of computing the estimated TSP annuity.