Extra Mortgage Payment / Early Payoff Calculator
See how much time and interest a recurring extra payment and/or a one-time extra payment saves on your mortgage.
How to Use
- Enter the loan amount, annual interest rate, and term in whole years.
- To model a recurring extra payment, enter the extra amount you'll add to every monthly payment — leave it at $0 to model a one-time extra payment only.
- To model a one-time extra payment (e.g. a bonus or tax refund applied to principal), enter its amount and which payment month it lands on — leave the amount at $0 to model a recurring extra payment only. You can also fill in both at once.
- The result compares your original payoff time and total interest against the payoff time and interest with your extra payment(s) applied, showing the time and interest saved.
Formula
- Normal payment
- payment = loan_amount × monthly_rate ÷ (1 − (1 + monthly_rate)^−months)
- Baseline simulation
- each month: interest = balance × monthly_rate; balance −= (payment − interest); repeat until balance reaches $0
- With extra payments
- same simulation, but each month also subtracts the recurring extra (and the one-time extra, only in its chosen month) directly from the balance, capped at what's still owed
- Savings
- months_saved = baseline_months − new_months; interest_saved = baseline_total_interest − new_total_interest
Worked Example
A $200,000 loan at 6% over 30 years, with an extra $200 added to every monthly payment.
- Normal monthly payment: ≈ $1,199.10
- Baseline payoff: 360 months, ≈ $231,676.38 total interest
- With an extra $200/month applied to principal every month: 252 months, ≈ $151,875.87 total interest
- Time saved: 360 − 252 = 108 months (9 years)
- Interest saved: $231,676.38 − $151,875.87 ≈ $79,800.51
Result: Original payoff time: 360 months (30 years) / New payoff time with extra payments: 252 months (21 years) / Time saved: 108 months (9 years) / Interest saved: $79,800.51
About This Tool
What this tool does
This calculator simulates your loan's normal month-by-month payoff, then simulates it again with a recurring extra monthly payment and/or a one-time extra payment applied directly to principal, and reports how much time and interest each scenario saves.
When to use it
Use it to decide whether a recurring extra payment fits your budget and is worth it, to see the effect of applying a windfall like a bonus or tax refund to your mortgage, or to compare a few different extra-payment amounts before committing to one.
What the result means
Time saved and interest saved reflect the exact same loan, rate and term in both scenarios — the only difference is the extra payment(s) — so the savings shown are a direct, apples-to-apples measure of what that extra money buys you.
Assumptions & limitations
Extra payments are assumed to go entirely toward principal, applied in the same month they're made, with no prepayment penalty — some real loans do charge one, so confirm your loan doesn't before relying on this. The recurring extra payment is assumed to continue every month until the loan is paid off; the one-time extra applies only in the single month you specify. This is an estimate based on the numbers you enter, not your servicer's exact payoff calculation.