The Inputs You Need
You need four numbers: your current loan balance (not original loan amount), your interest rate (from your monthly statement), your current monthly payment (principal + interest portion only, not escrow), and your proposed extra payment amount. Optional: remaining loan term (to see exact payoff date).
Extra payment calculator inputs and where to find them
| Input | Where to Find It | Common Error |
|---|---|---|
| Current balance | Monthly statement, mortgage servicer account | Using original loan amount instead of current balance |
| Interest rate | Monthly statement or loan documents | Confusing APR with monthly rate |
| Monthly P&I payment | Statement (exclude escrow for taxes/insurance) | Including escrow, which inflates the payment |
| Extra payment amount | Your budget decision | Being unrealistic about sustainable amount |
| Remaining term | Account page or amortization schedule | Guessing instead of checking exact remaining months |
The extra payment calculator needs your CURRENT remaining balance — not the original loan amount. If you took out a $280,000 mortgage 7 years ago, your current balance might be $245,000. Using $280,000 overstates payoff time and understates the impact of extra payments.
What the Output Tells You
Extra payment calculator output guide
| Output | What It Means | How to Use It |
|---|---|---|
| New payoff date | When you’ll own the home free and clear | Compare to current payoff date to see years saved |
| Interest savings | Total interest avoided by paying extra | The financial case for extra payments |
| Months shortened | How many months the loan is shortened | Convert to years for context |
| Break-even on extra payment | How long until cumulative savings exceed extra paid | Always positive immediately — no break-even needed |
A homeowner with a $240,000 balance at 6.5% with 22 years remaining who adds $200/month to her payment reduces her loan by 5 years and 4 months and saves $47,800 in interest. That $200/month commitment over 200 months saves $47,800 — a 900%+ return on every extra dollar contributed.
Calculate Your Exact Interest Savings
Enter your current balance, rate, and proposed extra payment to see years saved and total interest avoided.