Example 1 — Monthly overpayment
- Principal: 200,000
- Rate 6%, term 20 years
- Overpayment: +500/mo.
93 months earlier
Interest −61,565.25
An extra 500 a month shortens a 20-year loan by almost 8 years.
Loan overpayment calculator
See how many months earlier you pay off your loan and how much interest you save with an extra monthly payment or a one-time lump sum.
Enter the remaining loan principal, annual interest rate, and remaining term — the calculator computes the baseline amortizing payment, then compares it against an overpayment scenario. A monthly extra is added to the baseline payment from month one; a lump sum immediately reduces the principal. This is a simplified fixed-rate model with no early-repayment fees. Amounts follow the currency in the header.
Result
Enter data and click Calculate.
How results are calculated
Baseline payment = amortizing payment from the remaining principal, rate, and remaining term.
With overpayment: the starting principal is reduced by the lump sum, and the monthly extra is added to the baseline payment. We simulate the payoff month by month until the balance reaches zero.
Time saved = months earlier than the baseline. Interest saved = the difference in total interest between scenarios.
How to use the calculator
- Enter the remaining loan principal — check it in your amortization schedule or banking app.
- Enter the annual interest rate (%) and remaining term in years.
- Enter an extra monthly overpayment if you plan to pay more every month.
- Optional: open "One-time overpayment" to add a bonus, inheritance, or savings payment.
- Check how many months earlier you finish and how much interest you save.
Usage examples
Example 2 — One-time overpayment
- Principal: 150,000
- Rate 7.5%, term 15 years
- Lump sum: 20,000
39 months earlier
Interest −34,381.89
A lump sum lowers the principal immediately, and it shows up in every following payment.
Example 3 — Both overpayments together
- Principal: 80,000
- Rate 9%, term 10 years
- +200/mo. and a 5,000 lump sum
36 months earlier
Interest −15,465.63
Combining both strategies pays off faster than either alone.
FAQ
Which is better: a monthly extra payment or a lump sum?
Both reduce the balance and interest. A lump sum acts immediately across the whole remaining term, while a monthly extra compounds month over month — you can enter both and compare the result.
Does overpaying always shorten the term instead of lowering the payment?
It depends on your lender's terms — many default to shortening the term at the same payment (what this calculator assumes), others let you choose a lower payment at the same term instead.
Why does the calculator ask for the "remaining" balance and term, not the original loan?
Overpayment math only makes sense against your current balance right now, not the amount from years ago. Check these figures in your amortization schedule or banking app.
What if I don't enter any overpayment?
The result shows the baseline payment and a note that the schedule stays unchanged without an overpayment — enter an amount in the overpayment field to see the effect.
Can a lump sum exceed the remaining principal?
No — the calculator caps the lump sum below the remaining principal, since paying off the entire balance is a payoff, not an "overpayment."
Does my lender charge a fee for early repayment?
It depends on your contract and how far into the term you are — in many jurisdictions, overpayment fees are waived by law after a certain period. Check your loan agreement.
Will the interest rate change after overpaying?
The model assumes a fixed rate for the whole remaining term — a real variable rate will affect the result independently of the overpayment.
Why does currency follow the header?
Calcboxer keeps one currency for the whole page. Switching it in the header reformats result amounts.