Loan Prepayment Savings Calculator
A one-time lump sum payment applied to your loan principal reduces the outstanding balance immediately, cutting the interest that accrues on all future payments. This calculator compares two scenarios: paying only the regular monthly payment for the remaining term, versus making a one-time lump sum prepayment now and then continuing regular payments. The difference in total interest between the two scenarios is your prepayment savings.
Prepayment savings formula
Scenario A: simulate n months at balance B. Scenario B: simulate n months at balance (B - lump sum). Interest saved = Total Interest A - Total Interest B. Months saved = months A - months B.
Each scenario runs month by month: interest = balance * (APR/12/100); balance = balance + interest - payment. Stop when balance reaches zero. The prepayment scenario starts with the reduced balance.
ROI of a lump sum prepayment
The effective return on a loan prepayment equals the loan's APR, guaranteed. If your loan is at 7% APR, a $5,000 prepayment effectively earns 7% per year, tax-free (since you are avoiding interest cost, not earning taxable income). Compare this to your savings account yield, investment returns, or other uses of the $5,000 to decide whether prepayment is the best use of the funds.
Frequently asked questions
How does a lump sum prepayment save money?
A lump sum applied to principal reduces the balance immediately. Lower principal means less interest accrues each subsequent month. Over the remaining term, this compounds: you save not only the interest on the prepaid amount but also the cascading effect of a lower balance.
When is the best time to make a prepayment?
Early in a loan's life, when the balance is highest. A $5,000 prepayment made in month 1 of a 60-month loan saves more interest than the same prepayment made in month 48, because the balance has already been reduced by regular payments.
Does my lender have to apply prepayments to principal?
Under most loan agreements, you can designate extra payments as principal-only payments. However, some servicers may apply extra payments to future scheduled payments instead of reducing principal. Always specify in writing that extra payments should be applied to principal immediately.
Can I make partial prepayments?
Yes. Any extra amount paid beyond the regular monthly payment and interest obligation reduces principal. Consistent small extra payments can be as effective as occasional lump sums of the same total amount.
Are there prepayment penalties on consumer loans?
Most consumer loans in the US do not have prepayment penalties. However, some mortgage products (especially hard money loans and certain jumbo loans) may include them. Review your promissory note or loan agreement, and check the CFPB disclosure for any prepayment penalty information.
Official sources
- CFPB: Personal Loans.
- CFPB: Mortgages.
Reviewed by the CalculatorHub team, edited by James Graham, 15 June 2026. See our methodology.