Amortization Schedule Calculator
Generate a full amortization schedule with principal, interest, and balance by month.
An amortization schedule breaks every mortgage payment into its principal and interest components and tracks your outstanding balance month by month. Use this calculator to see exactly how much of each payment reduces your debt versus goes to the lender as interest — and to model the dramatic savings from even a small extra monthly prepayment.
Inputs
Optional additional payment each month
Results
Monthly Payment
$2,326
Total Interest
$297,926
Payoff Period
25y 0m
Interest Saved (vs no extra payment)
$0
Understanding This Calculator
See how each mortgage payment splits between interest and principal over time, and how small extra payments shorten the loan.
How the math works
Every month the lender first charges interest on the outstanding balance: Interest = Balance × effective monthly rate. Whatever is left of your fixed payment reduces the balance: Principal = Payment − Interest. Because the balance shrinks a little each month, the interest portion falls and the principal portion grows — slowly at first, faster near the end.
An extra monthly payment goes entirely to principal. That skips ahead on the schedule, so all future interest is charged on a smaller balance — which is why modest prepayments save a disproportionate amount of interest and cut months or years off the payoff date.
Worked example
With the defaults — a $400,000 loan at 5% over 25 years, semi-annual compounding — the payment is about $2,326.
- Month 1 interest: 400,000 × 0.4124% ≈ $1,650
- Month 1 principal: 2,326 − 1,650 ≈ $676
- New balance: about $399,324
Only about 29% of the first payment reduces the debt. Add an extra $200 per month and the loan pays off roughly three years sooner, saving tens of thousands in interest — the calculator shows the exact figure for your numbers.
How to read the result
Focus on three outputs:
- Total interest — the real cost of borrowing over the full amortization; it is often 60–75% of the original loan at today's rates.
- Payoff period — how the extra payment shortens the schedule.
- Interest saved — the dollar benefit of prepaying versus doing nothing.
Use the schedule to decide between prepaying and investing spare cash: prepaying earns a guaranteed, tax-free return equal to your mortgage rate. Check your lender's prepayment privileges first — many Canadian closed mortgages cap extra payments at 10–20% of the original balance per year.