An extra payment’s value is the interest it prevents — invisible until you actually run the loan’s normal schedule and its accelerated schedule side by side. This does exactly that.
Why extra payments save more early in a loan
Interest is calculated on the remaining balance, so a dollar of extra principal paid in year one avoids 29 more years of interest on that dollar; the identical extra dollar paid in year 29 avoids only one more year. This is the same mechanism the loan amortization calculator’s own article explains for why the payment split shifts toward principal over time — extra payments made early get the full benefit of that shift for the longest possible stretch.
How to use this calculator
- Enter your loan’s original terms.
- Enter how much extra you plan to pay each month.
- Read the time and interest saved.
Frequently asked questions
Is a biweekly payment plan the same as this?
Related — a common biweekly plan effectively adds one extra monthly payment a year (26 half-payments equal 13 full monthly payments), which you can model here by entering that extra amount averaged monthly.
Should I pay extra on my mortgage or invest the money instead?
This calculator only answers what extra payments save on this specific loan — it doesn’t compare that against what the same money might earn invested elsewhere, which depends on assumptions about investment returns this calculator doesn’t make.
Does my lender apply extra payments to principal automatically?
Not always — some lenders apply extra amounts to next month’s payment by default rather than directly reducing principal, unless you specify otherwise. Check with your servicer that extra payments are actually being applied the way you intend.
What if I can’t commit to the same extra amount every month?
This models a fixed extra payment throughout. An irregular extra payment (occasional lump sums, for instance) will save a different amount — generally less predictable, but the same underlying principle: paid earlier saves more.
Why does the interest saved number often look larger than expected?
Because it compounds over the full remaining life of the loan — a relatively modest monthly extra payment, sustained for years, ends up preventing a large amount of the interest that would otherwise have accrued on a shrinking-but-still-substantial balance.
