5 CFR 1655.17 - Prepayment.
(a) A participant may repay a loan in full, without a penalty, at any time before the declaration of a taxable distribution under § 1655.15, unless the participant has separated from Government service and has submitted a signed statement that he or she has forfeited the right to repay the loan in full. Repayment in full means receipt by the TSP record keeper of a payment, by personal check or guaranteed funds made payable to the Thrift Savings Plan, of all principal and interest due on the loan.
(b) If a participant returns a loan check to the TSP record keeper, it will be treated as a repayment; however, additional interest may be owed, which, if not paid, could result in a taxable distribution. The loan, even though repaid, will also be taken into account in determining the maximum amount available for future loans, in accordance with § 1655.6(b).
(c) The amount outstanding on a loan can be obtained from the TSP Web site, the ThriftLine, or a TSPSO participant service representative, or by a written request to the TSP record keeper.