Quick answer
Quick answer
The interest rate differential, or IRD, is one of two prepayment penalties that can apply when you break a closed fixed-rate mortgage before its term ends. It estimates the interest your lender loses by re-lending your money at today's rate, calculated as the gap between your contract rate and a current comparison rate, applied to your balance over the months remaining in your term. On a closed fixed-rate mortgage you pay the greater of three months' interest or the IRD; when current rates sit below your contract rate, the IRD is usually the larger figure. Big-6 banks typically use posted rates in the calculation, which can make the penalty several times higher than the discounted-rate method most monoline lenders use. IRD does not apply to closed variable-rate mortgages, which use three months' interest, and it does not apply at mortgage renewal.
The payout quote that doesn't match what you expected
You called your lender to ask what it would cost to break your mortgage, and the number that came back was nothing like what you planned for. You expected a few thousand dollars. The figure was three or four times higher.
That gap usually has one cause: the interest rate differential, or IRD. It is the penalty that makes a fixed-rate mortgage expensive to leave early, and most Canadians never hear about it until the day they ask.
The good news is that the IRD is not random. It follows a formula you can learn, check, and sometimes push back on. Once you understand the two rates behind it and the one choice your lender makes, that intimidating number starts to make sense. This guide walks through how the IRD works, using one example you can map onto your own mortgage.
Pick your path: which penalty are you dealing with?
Before the math, find your situation. The penalty you face depends on the type of mortgage you hold.
If you are in the first group, the rest of this article is where your money is.
What the interest rate differential actually is
When you signed a fixed-rate mortgage, your lender committed to that rate for your whole term and planned around the interest you agreed to pay. If you leave early while rates have fallen, the lender re-lends that money at a lower rate and earns less. The IRD recovers the difference.
This is why the IRD only applies to closed fixed-rate mortgages. Variable-rate mortgages use a simpler three months' interest charge, and open mortgages carry no penalty. For the full picture of every penalty type, see our guide to how Canadian prepayment penalties work.
One definition worth keeping: a prepayment penalty is the fee a lender charges when you pay off all or part of a closed mortgage ahead of schedule.
The two rates behind every IRD calculation
Your contract rate is the easy part. It is the rate you have been paying, and it sits on your mortgage statement.
The comparison rate is where lenders differ. It represents what the lender could earn today by lending your balance for the months you have left. A shorter remaining term points to a different comparison rate than a longer one, because lenders match the rate to the time left.
The remaining term matters too. The more months left, the longer the lender's lost interest stretches, and the larger the IRD grows. Two mortgages with identical balances and rates can land at very different penalties simply because one has more time remaining.
Posted-rate vs discounted-rate IRD: where the big penalties come from
Here is the part most Canadians never see coming. When you got your mortgage, your lender likely advertised a posted rate, the official sticker rate, then gave you a discount off it. If the posted rate was 6.80% and you signed at 5.50%, your discount was 1.30%.
Many large banks calculate the IRD by taking today's posted rate for your remaining term and subtracting that original 1.30%. That lowers the comparison rate, widens the gap against your contract rate, and pushes the penalty up.
Most monoline lenders, which only offer mortgages and do not run retail branches, skip that step. They compare your rate to today's actual discounted rate, which keeps the gap closer to the real market difference and the penalty smaller.
The mortgage can be identical: same balance, same rate, same months remaining. The penalty still lands thousands of dollars apart, decided only by the comparison rate. A posted rate is the lender's publicly advertised, non-discounted rate, almost always higher than the rate borrowers actually pay.
| Detail | Big-6 posted-rate method | Monoline discounted-rate method |
|---|---|---|
| Outstanding balance | $350,000 | $350,000 |
| Your contract rate | 5.50% | 5.50% |
| Comparison rate the lender uses | 2.90% posted 4.20% minus your 1.30% discount | 4.20% today's discounted rate |
| Rate gap that drives the penalty | 2.60% | 1.30% |
| Months remaining in term | 36 | 36 |
| Estimated IRD penalty | $27,300 | $13,650 |
A worked IRD calculation, step by step
Put real numbers to it. Imagine a $350,000 balance at a contract rate of 5.50%, with 36 months left on a five-year term. At signing the posted rate was 6.80%, so the original discount was 1.30%. Today's posted three-year rate is 4.20%. These figures are illustrative, but the method is what lenders use.
First, the posted-rate method many big banks apply. Take today's 4.20% and subtract the original 1.30% discount, giving a comparison rate of 2.90%. The gap against your 5.50% rate is 2.60%. Multiply: $350,000 times 2.60% times three years equals roughly $27,300.
Now the discounted-rate method most monoline lenders use. Compare your 5.50% directly to today's 4.20%, for a gap of 1.30%. Multiply: $350,000 times 1.30% times three years equals roughly $13,650.
Same mortgage, a difference of about $13,650, driven only by the comparison rate.
You can run these numbers for your own mortgage with our prepayment penalty calculator before you call your lender. Treat the result as an estimate to check the official figure against, not a final quote.
IRD or three months' interest: which figure you actually pay
Three months' interest is the simple calculation: your balance times your contract rate, divided by four. On our $350,000 example at 5.50%, that comes to about $4,800.
Your lender works out both figures and charges whichever is higher. Because both IRD results in our example, $13,650 and $27,300, sit well above $4,800, the IRD is what applies.
There is also a federal limit worth knowing. If your mortgage term is longer than five years, the Interest Act caps the penalty at three months' interest once five years have passed since you signed. For the common five-year term, that cap does not come into play.
| Mortgage type | Penalty method | Does IRD apply? | Typical size |
|---|---|---|---|
| Closed fixed-rate | Greater of three months' interest or IRD | Yes | Often the largest |
| Closed variable-rate | Three months' interest | No | Usually modest |
| Open (fixed or variable) | No penalty | No | Nil |
How to check and challenge your payout statement
Your lender must give you a written payout statement, sometimes called a discharge statement, if you ask. This is the binding figure. Request it before you decide anything, because an online estimate is only a starting point.
When it arrives, check three things: the comparison rate used, whether your original discount was subtracted, and how many months they counted as remaining. An error in any of them changes the number.
If the figure looks higher than your own estimate, ask the lender to explain the comparison rate and confirm the method. Our walkthrough on using a penalty calculator correctly shows how to build a number you can hold them to.
This is where a broker earns their keep. Razi Khan, Founder and Mortgage Broker at Pegasus has spent years reading these statements and spotting where a posted-rate calculation has quietly inflated a penalty. Sometimes a few questions, or a switch to a fairer lender at renewal, saves thousands.
Common mistakes that make an IRD penalty worse
A few avoidable missteps can cost more than the penalty itself:
- ▸Assuming the penalty is three months' interest. On a fixed-rate mortgage with rates down, the IRD is often far larger.
- ▸Breaking just before renewal. At renewal you can leave with no penalty, so timing the move by a few weeks can save the entire IRD.
- ▸Ignoring portability. Many mortgages let you carry your existing rate to a new home and sidestep the penalty. See ways to avoid an expensive break penalty.
- ▸Forgetting your annual prepayment privilege. Paying down the allowed lump sum first shrinks the balance the penalty is based on.
- ▸Taking the first number as final. It is an estimate until you have the written statement.
- ▸Overlooking added costs. Discharge fees, legal costs, and cashback clawbacks can stack on top of the IRD.
Frequently asked questions
What is the interest rate differential on a mortgage?
Why is my mortgage penalty so much higher than three months' interest?
How do banks actually calculate the IRD?
What's the difference between posted-rate and discounted-rate IRD?
Does the IRD penalty apply to a variable-rate mortgage?
Do I have to pay an IRD penalty when I renew my mortgage?
Can I lower or avoid an IRD penalty?
How can I check whether my IRD penalty is correct?
The bottom line on your IRD penalty
The interest rate differential can make breaking a fixed-rate mortgage expensive, but it is not a mystery. It comes down to two rates, the months you have left, and the comparison rate your lender chooses. Once you can see those pieces, you can check the math and ask the right questions before signing anything away.
See your real numbers before you decide
Pegasus shops more than 50 lenders to find fair penalty terms and the right exit. Get an instant pre-approval and let us review your payout before you break.
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About the author
Razi Khan
Founder, CEO & Licensed Mortgage Broker · Pegasus Mortgage Lending · Toronto, Ontario · FSRA Lic # 11479
Razi Khan is the Founder, CEO, and a licensed Mortgage Broker at Pegasus Mortgage Lending Center Inc., based in Toronto. With over 20 years of experience in the Canadian mortgage industry, Razi has personally guided more than 3,000 clients through some of the most complex and high-stakes financial decisions of their lives — from first-time purchases in the GTA to refinancing strategies, alternative lending solutions, and cross-border mortgages for Canadians buying in the United States.
Razi founded Pegasus in October 2008, launching the brokerage at the height of a global financial crisis. He works across the full spectrum of borrower profiles, with particular expertise in complex files including self-employed borrowers, credit-challenged clients, and investors building multi-property portfolios.
Learn more about Razi Khan →Sources & references
- Financial Consumer Agency of Canada — Reduce your prepayment penalties. canada.ca
- Interest Act (Canada), R.S.C. 1985, c. I-15, s. 10. laws-lois.justice.gc.ca
- Bank of Canada — Policy interest rate. bankofcanada.ca