How do most Big Banks in Canada Calculate the Penalty to break a mortgage?
March 28 2026
The Interest Rate Differential (IRD) penalty is notorious for being expensive and confusing, primarily because major banks don’t just compare your current rate to today's rates—they use a "Posted Rate" calculation that often inflates the fee.
Here is the step-by-step breakdown of how they do it.
The 4 Key Ingredients
To calculate this, a bank looks at four specific numbers:
- Your Current Mortgage Rate: The actual interest rate you are paying (the "Contract Rate").
- The Original Discount: The difference between the Posted Rate when you signed and the Contract Rate you actually got.
- The Current Posted Rate: The bank’s current advertised rate for a term that matches your remaining time (e.g., if you have 2 years left on a 5-year mortgage, they look at the current 2-year posted rate).
- The Comparison Rate: This is the "Current Posted Rate" minus your "Original Discount."
The Step-by-Step Formula
Banks use the Comparison Rate to determine how much interest they are "losing" by letting you out of your contract early.
1. Find the Comparison Rate: Current Posted Rate (for remaining term)} - Your Original Discount} = Comparison Rate
2. Find the Interest Gap (The Differential): Your Current Rate - Comparison Rate = The IRD
3. Calculate the Total Penalty: Remaining Balance x The IRD x Months Left on Term
A Concrete Example
Imagine you have a $400,000 mortgage balance with 3 years (36 months) left on your term.
- Your Rate: 3.5%
- Original Discount: When you signed, the posted rate was 5.5%, but you got 3.5% on your mortgage (a 2.0% discount).
- Today’s 3-Year Posted Rate: Let’s say the bank currently advertises a 3-year term at 4.2%.
The Calculation:
- Comparison Rate: $4.2% - 2.0% = 2.2%
- Interest Gap: $3.5% - 2.2% = 1.3
The Penalty:
- $400,000 x 0.013 x 36 / 12 = $15,600
Why the "Posted Rate" Method is Controversial
If the bank simply compared your 3.5% rate to a current 3.5% market rate, your penalty would be $0 (or the standard 3 months' interest).
However, by subtracting your Original Discount from a current Posted Rate, they artificially lower the "Comparison Rate." This creates a wider gap between what you are paying and what they claim they can lend the money out for now, which significantly hikes the penalty.
Summary Table
| Feature | Standard IRD | Posted Rate IRD (BANK) |
|---|---|---|
| Comparison Rate | Current Market Rate | Current Posted Rate minus Original Discount |
| Penalty Size | Generally Lower | Often 2-3x Higher |
| Used By | Broker Lenders | "Big 5" banks |
Pro Tip: Banks almost always charge the greater of the IRD penalty or three months' interest. If interest rates have gone up since you signed your mortgage, the IRD will likely be $0, and you'll just pay the three months' interest. If rates have gone down, prepare for the IRD. Ask your Mortgage Managers broker about lenders that don't use a Posted Rate to calculate the IRD Penalty.
