Last updated October 10, 2026 · Report an error
A little extra paid toward the principal each month can shave years off a mortgage and save thousands in interest — but it helps to see the actual numbers before committing to it.
This calculator compares your standard payoff schedule against one with an extra monthly payment, showing the months and interest saved.
How it works
Enter your remaining loan balance, annual interest rate, remaining term in months, and the extra amount you plan to pay each month. The calculator simulates both amortization schedules month by month and reports the difference.
- Enter remaining loan balance ($).
- Enter annual interest rate (%).
- Enter remaining term (months).
- Enter extra monthly payment ($).
- Click Calculate to see your results.
Examples
$200,000 balance, $200 extra
A $200,000 balance at 6% with 300 months remaining pays off about 77 months sooner and saves roughly $54,000 in interest by adding $200 to every monthly payment.
Who should use it
- Deciding whether to direct extra cash toward mortgage principal.
- Comparing different extra-payment amounts to see the impact on payoff time.
Industry applications
- Personal mortgage and debt planning
- Financial advising
Advantages
- Shows both months saved and total interest saved in one calculation.
- Simulates the full amortization schedule rather than using an approximation.
Limitations
- Assumes a constant extra payment every month for the life of the loan.
Common mistakes to avoid
- Assuming extra payments automatically reduce principal without confirming this with the loan servicer.
- Not accounting for prepayment penalties that may apply to some loans.
Best practices
- Confirm with your lender that extra payments are applied directly to principal, and mark the payment accordingly when you submit it.
Tips
- Even a modest, consistent extra payment compounds significantly over a 15-30 year mortgage — try a few different amounts to see the trade-off.