Prepayment savings.

Why prepayment matters

Every extra dollar applied directly to principal saves you years of compound interest. Most Canadian lenders allow 10%–20% lump-sum prepayments and a 10%–20% increase in regular payments each year without penalty.

Why prepaying early is worth so much more than prepaying late

A mortgage payment is a fixed amount split between interest and principal, and the split changes every single month. Early on, almost all of it is interest, because interest is charged on a large outstanding balance. By the end, almost all of it is principal.

A lump sum goes 100% to principal, which means it removes that balance from every future interest calculation for the remaining life of the loan. Prepay $10,000 in year two of a 25-year mortgage and you avoid interest on that $10,000 for twenty-three years. Prepay the same $10,000 in year twenty-two and you avoid three years of it. Same money, wildly different result, which is why the strongest single argument for prepaying is simply that it is early.

The corollary is worth stating plainly: the guaranteed, tax-free return on a mortgage prepayment equals your mortgage rate. There is no risk and no tax on it, which makes it a genuinely hard return to beat with anything other than high-interest debt repayment or an employer pension match.

Canadian mortgage maths is not American mortgage maths

Section 6 of the federal Interest Act requires that a mortgage with blended payments of principal and interest state the rate calculated yearly or half-yearly, not in advance. In practice Canadian fixed-rate mortgages are compounded semi-annually, while American ones are compounded monthly.

The consequence is small per payment and large over an amortisation: a nominal 5% compounded semi-annually is a lower effective rate than a nominal 5% compounded monthly, so the Canadian payment on the same balance, rate and amortisation is slightly lower. Any calculator that quietly uses monthly compounding (which is most of the ones written for a US audience) overstates a Canadian payment and misstates the interest saved by a prepayment. It is a genuine reason to distrust a figure from a US mortgage tool.

The two penalties, and which one you are exposed to

Prepayment privileges are a contractual feature of your specific mortgage, not a statutory right. Exceed them, or break the mortgage entirely, and a prepayment charge applies. There are two formulas and the difference between them can be tens of thousands of dollars.

Three months’ interest

Exactly what it says: roughly three months of interest on the amount being prepaid. This is the charge that typically applies to a variable-rate mortgage, and it is the predictable, survivable one.

The interest rate differential

On a fixed-rate mortgage, lenders normally charge the greater of three months’ interest and an interest rate differential: the IRD. The IRD is meant to compensate the lender for the interest it loses by re-lending your money at a lower rate: broadly, the gap between your rate and the lender’s current rate for a term matching what you have left, applied to the amount prepaid, for the time remaining in your term.

Two things make the IRD dangerous rather than merely annoying. First, it scales with how much time is left, so breaking a five-year fixed in year two is far more expensive than breaking it in year four, and in the last few months of a term, an IRD is often close to nothing. Second, and much less well understood: several of the large Canadian banks calculate the IRD using posted rates and the discount you originally negotiated, rather than the rates you actually contracted at. Because posted rates are usually well above real market rates, that method can produce a penalty many times larger than an intuitive rate-difference calculation suggests. Monoline lenders more commonly use contract rates, which is a real and frequently overlooked difference between two mortgages at the same rate.

The practical instruction: before you prepay above your privilege, or break a mortgage, phone the lender and ask for the exact charge in writing along with the formula used. Do not estimate it. Lenders are required to disclose how they calculate it, and the number is often not what the arithmetic in your head produces.

Using the privileges properly

• They usually do not carry over. An unused allowance is generally lost at the end of the year, so a smaller prepayment made every year beats a large one made once.
• Check when you are allowed to use them. Some contracts permit a lump sum at any time, others only on the anniversary date, and some cap the number of separate payments. Missing an anniversary window costs you a full year of allowance.
• Percentage of original principal. Privileges are commonly expressed against the original loan amount rather than the current balance, which quietly makes the allowance more generous as the balance falls.
• Payment increases compound harder than lump sums. A permanent increase applies to every remaining payment; a lump sum applies once. If you can only do one and the money is recurring, raise the payment.
• Accelerated bi-weekly is a prepayment in disguise. Take the monthly payment, halve it, pay it every two weeks: 26 payments a year is thirteen monthly equivalents rather than twelve. You have made one extra full payment a year without ever deciding to, and it typically removes years from a 25-year amortisation. It is the single easiest prepayment to set up because it requires no ongoing discipline.

Prepay, or invest, or contribute?

Prepaying is a guaranteed after-tax return equal to your rate. Compare it against the after-tax return you would realistically get elsewhere, not the gross one, and take the ordering seriously:

• High-interest debt first, always. Credit cards and unsecured lines at double-digit rates beat a mortgage prepayment by a wide margin. The debt payoff calculator sequences them.
• Any employer pension or RRSP match. A match is an immediate guaranteed return no mortgage rate approaches.
• Then it is genuinely close. Against a mortgage in the low single digits, a long-horizon TFSA or RRSP contribution has historically won on expected value while carrying risk and volatility that a prepayment does not. Against a mortgage at 5% or more, prepaying is a strong and certain choice. There is no universally correct answer, only your rate, your marginal tax rate and how much certainty you want.

One Canadian wrinkle worth knowing: mortgage interest on your own home is not deductible here, unlike in the United States, which is precisely why prepaying it is more attractive in Canada than the American commentary suggests. The strategy built on that asymmetry (converting non-deductible mortgage debt into deductible investment debt) is the Smith Manoeuvre, and it is a genuine alternative use for the same cash flow.

If you are breaking the mortgage rather than prepaying

Three options that are not “pay the penalty” and are often not offered unless you ask. Porting moves your existing mortgage and rate to a new property, avoiding the charge entirely. Blend and extend merges your existing rate with a current one into a new longer term, spreading the cost instead of charging it up front: convenient, and worth calculating rather than accepting, because the blended rate embeds the penalty. And if you are simply near the end of the term, waiting a few months until renewal can reduce an IRD to almost nothing.

Related: mortgage payment for the base payment, amortisation for the full schedule, and refinance to weigh a break cost against a lower rate.