A prepayment penalty is a charge, which makes it a different thing from an unrefunded interest rebate. On a precomputed loan, interest for the whole term is written into the note at the outset, so paying early raises the question of how much of that interest the borrower gets back. That is a refund question, governed by its own federal rules, and published material on amortization sets those out. A prepayment penalty is an affirmative charge on top of what is owed. A borrower can face either, both, or neither, and a loan document that mentions a "prepayment charge" may be describing whichever one applies.
Regulation Z rations mortgage prepayment penalties, and this is the part almost no borrower knows. The rules at 12 CFR 1026.43(g) apply to a covered transaction, meaning a consumer credit transaction secured by a dwelling (1026.43(b)(1)). They work in three layers.
Under (g)(1), such a loan must not include a prepayment penalty unless the penalty is otherwise permitted by law and the transaction has an annual percentage rate that cannot increase after consummation, is a qualified mortgage, and is not a higher-priced mortgage loan as defined in 12 CFR 1026.35(a). In plain terms: no adjustable-rate loan, no subprime-priced loan, and no loan outside the qualified mortgage perimeter may carry one.
Under (g)(2), where a penalty is permitted, it "must not apply after the three-year period following consummation" and "must not exceed the following percentages of the amount of the outstanding loan balance prepaid": 2 percent if incurred during the first two years after consummation, and 1 percent if incurred during the third year. After three years there can be no penalty at all.
Under (g)(3), the creditor "must not offer a consumer a covered transaction with a prepayment penalty unless the creditor also offers the consumer an alternative covered transaction without a prepayment penalty." The alternative has to be genuine: the same type of interest rate, fixed or step-rate, with a rate that cannot increase after consummation; the same loan term; payments meeting the qualified mortgage conditions; points and fees within the qualified mortgage limits; and a good-faith belief by the creditor that the consumer is likely to qualify for it. Where the loan is offered through a mortgage broker, (g)(4) requires the creditor to present the alternative to the broker and to bind the broker by agreement to present it to the consumer. So on a mortgage, a prepayment penalty is something a borrower can decline, usually in exchange for a different rate, and the offer of the penalty-free version is not optional for the lender.
The high-cost mortgage rules approach the same charge from the opposite direction, and the numbers line up. A loan is a high-cost mortgage if, among other tests, "the creditor can charge a prepayment penalty, as defined in paragraph (b)(6) of this section, more than 36 months after consummation or account opening, or prepayment penalties that can exceed, in total, more than 2 percent of the amount prepaid" (12 CFR 1026.32(a)(1)(iii)). And a high-cost mortgage may not include a prepayment penalty at all (1026.32(d)(6)). Read together, the two provisions form a closed loop: a penalty beyond 36 months or above 2 percent makes the loan high-cost, and a high-cost loan may not have a penalty. That is the mechanism by which the outer limits are enforced rather than merely stated.
How to find out whether a loan has one. For closed-end credit generally, 12 CFR 1026.18(k) requires a statement of whether a charge may be imposed for paying the principal early where interest is computed on the unpaid balance, and, where it is not, a statement of whether the borrower is entitled to a rebate of the finance charge on prepayment. On a mortgage, 12 CFR 1026.37(b)(4) puts the answer in the "Loan Terms" table on the Loan Estimate, labeled "Prepayment Penalty", and repeats the definition so the label cannot be applied loosely. Those are the lines to read before signing, because a penalty found afterwards cannot be negotiated.
Outside the dwelling-secured perimeter, Regulation Z's rationing does not reach. 12 CFR 1026.43 applies by its own terms to consumer credit secured by a dwelling, so a car loan, a personal loan or a student loan is governed instead by its contract, by any product-specific federal rule, and by state law, which varies. Whether a particular loan permits a charge for early payoff is therefore a document question rather than a rule question, and the 1026.18(k) disclosure is where a closed-end contract has to answer it.