Semi-Annual Compounding

Semi-annual compounding is the Canadian convention in which a mortgage interest rate quoted as an annual percentage is compounded twice a year: interest is calculated on the outstanding balance and added to it every six months, rather than being compounded monthly or daily. It is the standard basis on which fixed-rate mortgage rates are quoted and compared in Canada.

How semi-annual compounding works

When a lender advertises a fixed rate, that figure is a nominal annual rate compounded semi-annually. Under this convention the balance is charged interest every six months at half the stated annual rate. The effective annual rate is therefore slightly higher than the quoted rate, and can be expressed as (1 + nominal rate ÷ 2)² − 1.

More frequent compounding raises the effective rate on the same nominal figure:

Semi-annual — interest added twice a year, the Canadian mortgage standard.
Monthly — interest added twelve times a year, which increases the effective annual rate.
Annual — interest added once a year, which gives the lowest effective rate for a given nominal figure.

The gap is small but real, and it matters most when two offers are quoted under different conventions. The effective annual rate is the clearest basis for comparison.

Why it matters to borrowers

Monthly payments on a fixed-rate mortgage spread interest over the year, so a borrower never actually waits six months to pay. The semi-annual convention governs how interest accrues behind the scenes and therefore the true cost of borrowing. It also feeds into prepayment penalties, since three months' interest and interest rate differential calculations both depend on how the rate is expressed — which is part of why penalty quotes can differ between lenders.

It does not apply to every product

Variable-rate mortgages and home equity lines of credit are commonly compounded monthly instead, so their effective cost runs a little higher than the quoted nominal rate for the same figure. Federal cost-of-borrowing disclosure rules require lenders to present an annual percentage rate that reflects compounding, which lets borrowers compare a fixed and a variable offer on a like-for-like basis. The difference in compounding is one of several factors worth weighing when choosing between rate types.

For a fuller walkthrough, see the guide on why Canadian mortgages compound semi-annually.

Frequently asked questions

Does semi-annual compounding mean I only pay interest twice a year?

No. Most Canadian fixed-rate mortgages are paid monthly, bi-weekly, or weekly. Semi-annual compounding describes how interest is calculated and added to the balance, not how often you make a payment. Your regular payment amount already reflects the compounding convention used by the lender.

Is semi-annual compounding better for borrowers than monthly compounding?

For the same nominal rate, semi-annual compounding produces a slightly lower effective annual rate than monthly compounding, so the true cost of borrowing is a little lower. That is why the effective rate, not just the advertised rate, is the sound basis for comparing offers from different lenders.

Do variable-rate mortgages use semi-annual compounding?

Typically no. Variable-rate mortgages and home equity lines of credit in Canada are commonly compounded monthly, while fixed-rate mortgages generally follow the semi-annual convention. Because lenders must disclose an annual percentage rate that accounts for compounding, the two can still be compared on a common basis.