How Much Can Mortgage Prepayments Actually Save?
Prepayments save interest at your full mortgage rate, so a $5,000-per-year extra payment on a $500,000 mortgage at 4.59% over 25 years saves roughly $77,000 in interest and cuts about 5 years off the amortization. Those are approximate figures — your actual savings depend on timing and your lender's terms. Most lenders allow annual lump-sum prepayments of 15–20% of the original balance without penalty, but exceeding the limit triggers prepayment penalties that differ sharply between fixed and variable mortgages.
How the savings work
Every extra dollar you put toward the mortgage reduces the principal, which means less interest accrues on every payment after that. Because interest is front-loaded in an amortizing loan, early prepayments have an outsized effect.
Using the $500,000 / 4.59% / 25-year example: adding $5,000 once a year (on top of regular payments) saves roughly $77,000 in total interest and shortens the loan by about 5 years. The math behind it is straightforward — each $5,000 lump sum saves roughly 4.59% of that amount per year for the remaining life of the mortgage, compounding into a large lifetime saving.
The earlier in the mortgage you prepay, the bigger the effect: $5,000 in year 2 saves more interest than the same $5,000 in year 20, because it has longer to compound.
Know your lender's prepayment privileges
Most Canadian lenders allow you to prepay 15–20% of the original mortgage balance per year as a lump sum without penalty, plus options to increase your regular payment by a set amount (often 15–100% of the payment) or double up individual payments. The exact percentages are in your mortgage contract — they are not the same at every lender.
Penalties: the number you must not exceed
Going beyond your prepayment privilege triggers a penalty:
| Mortgage type | Penalty |
|---|---|
| Variable rate | 3 months' interest |
| Fixed rate | The greater of 3 months' interest or the interest rate differential (IRD) |
The IRD on a fixed mortgage can be substantial — it is based on the difference between your contracted rate and the rate your lender could now charge for a similar term, applied to the remaining balance and term. On a large balance with years left in the term, the IRD can reach tens of thousands of dollars, which often wipes out the benefit of breaking the mortgage.
When prepaying may not be the best use of cash
Prepayments earn you a guaranteed, after-tax return equal to your mortgage rate. That is excellent when rates are high and you are carrying non-deductible debt — but compare it against alternatives: higher-interest debt (credit cards first), underfunded retirement savings, or an emergency fund. There is no single right answer; there is a comparison.
Frequently asked questions
Can I prepay if my mortgage is closed?
A closed mortgage still has annual prepayment privileges (typically 15–20% of the original balance as a lump sum). "Closed" means you cannot pay the whole thing off or break it cheaply mid-term — not that extra payments are forbidden.
Does the lump-sum allowance reset each year?
Yes — the annual prepayment privilege is per anniversary year of the mortgage. Unused room does not carry forward, so use-it-or-lose-it applies.
What is the interest rate differential (IRD)?
The IRD is the difference between the interest your lender would have earned on your mortgage for the rest of the term and what it can earn re-lending the money at today's rate. Lenders each use their own formula, which is one reason fixed-rate break penalties vary so much — and why you should ask your lender for a written penalty quote before making a large prepayment beyond your privileges.
Should I prepay or invest instead?
If your mortgage rate is 4.59%, prepaying gives a guaranteed, risk-free return of 4.59% after tax. Investing may beat that, but with market risk. The cleaner comparison: your mortgage rate is the hurdle rate your investments must beat after tax and after risk.
Canadian Mortgage Calculator 2026 — CA$29
Model prepayments against your own mortgage with the Canadian Mortgage Calculator 2026.
Sources
- Financial Consumer Agency of Canada, Preparing for your mortgage — prepayment privileges and penalties: https://www.canada.ca/en/financial-consumer-agency/services/mortgages/preparing-mortgage.html
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