A blended mortgage rate is what you get when your lender combines two interest rates into a single weighted-average rate on one mortgage. The usual case is borrowing more mid-term: you have an existing mortgage at one rate and need additional funds, so the lender blends your old rate with today’s rate according to the dollar amounts involved. The result sits between your existing rate and the current rate, and your existing maturity date stays the same (a “blend to term”). This page is part of our guide to mortgage types and features.
The other version, blend and extend, also resets the term to a new full period, so the blend is weighted by time as well as dollars and you commit to the lender for longer. This page covers only the blend to term.
When Blended Rates Come Into Play
| Scenario | What happens |
|---|---|
| Mid-term increase | You need more money before your term matures; the lender blends old and new rates |
| Porting with an increase | You sell and buy, and the new home needs a larger mortgage; the old rate blends with the new |
| Consolidation | Combining a mortgage and HELOC into one product at a blended rate |
| Assumed mortgage with additional funds | A buyer assumes the seller’s mortgage and needs more; the lender blends |
The most common use is the mid-term increase: borrowing more against your home for renovations, debt consolidation or other purposes without breaking your existing mortgage and paying the penalty.
How the Blended Rate Is Calculated
The Weighted Average Formula
Blended Rate = (Balance₁ × Rate₁ + Balance₂ × Rate₂) ÷ (Balance₁ + Balance₂)
Example: Mid-Term Increase
| Component | Amount | Rate |
|---|---|---|
| Existing mortgage balance | $350,000 | 3.89% |
| New additional funds | $100,000 | 5.49% |
| New total balance | $450,000 | ? |
Calculation:
($350,000 × 3.89% + $100,000 × 5.49%) ÷ $450,000
= ($13,615 + $5,490) ÷ $450,000
= $19,105 ÷ $450,000
= 4.25%
In this example the blended rate of 4.25% is well below the 5.49% it would cost to refinance the whole $450,000 at the new-funds rate.
Payment Comparison
| Option | Rate | Monthly Payment | Monthly Difference |
|---|---|---|---|
| Blended rate increase | 4.25% | $2,428 | Baseline |
| Full refinance at the new-funds rate | 5.49% | $2,744 | +$316/month |
| Difference over 3 years remaining | $11,364 |
25-year amortization on $450,000, semi-annual compounding.
The blend also avoids the prepayment penalty on the existing $350,000, which on a fixed-rate mortgage can run to five figures. Breaking a closed mortgage, paying it off early or prepaying more than your privileges allow usually costs the higher of 3 months' interest and the interest rate differential (IRD) on a fixed rate, and typically 3 months' interest on a variable rate; your mortgage contract sets the exact method and comparison rate, and a federally regulated lender must tell you how it calculates the penalty. The full method is in how mortgage penalties are calculated.
Blended Rate When Porting With an Increase
When you sell and buy mid-term, many lenders let you move the mortgage to the new property. If the new home costs more, the extra funds are added at today’s rate and blended with the ported balance. The porting process itself (deadlines, requalifying, what happens if the sale and purchase don’t line up) is covered in how to port a mortgage.
Example: Porting With an Increase
| Component | Details |
|---|---|
| Current mortgage | $380,000 at 3.69%, 2 years remaining |
| Sale price (current home) | $550,000 |
| Purchase price (new home) | $750,000 |
| New mortgage needed | $530,000 |
| Ported mortgage | $380,000 at 3.69% |
| New funds | $150,000 at 5.29% (the lender’s 2-year rate in this example) |
Blended Rate:
($380,000 × 3.69% + $150,000 × 5.29%) ÷ $530,000
= ($14,022 + $7,935) ÷ $530,000
= 4.14%
Alternative: Break and Take a New Mortgage
| Cost Component | Amount |
|---|---|
| Prepayment penalty (IRD) | $12,500 |
| New mortgage: $530,000 at 5.29% (25-year amortization) | $3,171/month |
| Blended mortgage: $530,000 at 4.14% (25-year amortization) | $2,828/month |
| Monthly savings with blend | $342/month |
| Savings over 2 years remaining | $8,215 |
| Total benefit of blending | $8,215 savings + $12,500 penalty avoided = $20,715 |
In this case, porting and blending saves over $20,000 compared with breaking the mortgage and starting fresh.
Who Offers a Blend to Term
Availability varies by lender and by product. Some lenders offer a blend to term on a mid-term increase, others offer only blend and extend, and some won’t add funds mid-term at all and require a refinance instead. Before choosing a lender, it is worth asking which of these it allows if you expect to need more money during the term.
When a Blended Rate Makes Sense
Situations where blending tends to work
| Situation | Why blending works |
|---|---|
| Your existing rate is well below current rates | The weighted average beats the new-funds rate by a wide margin |
| You need modest additional funds | The blend stays weighted toward your low existing rate |
| High prepayment penalty | Avoiding the penalty makes blending clearly cheaper |
| Porting to a more expensive home | Your ported rate blends with the new funds |
| 1-2 years left on the term | The penalty is lower, but blending still avoids it entirely |
Situations where it doesn’t
| Situation | Why blending doesn’t work |
|---|---|
| Your existing rate is close to or above current rates | Little benefit to blending; a refinance may suit better |
| You need a very large increase | New funds dominate the blend, so the result is close to the current rate anyway |
| You want to switch lenders | Blending is only available with your current lender |
| You want a longer amortization | A blend to term usually keeps your amortization; a refinance can lengthen it |
The Math: When Does Blending Stop Making Sense?
The answer depends on how much you are borrowing relative to your existing balance and on the gap between the two rates.
Blended Rate by New Funds as % of Total
| Existing Rate | New-Funds Rate | New Funds = 10% | New Funds = 25% | New Funds = 50% | New Funds = 75% |
|---|---|---|---|---|---|
| 3.50% | 5.50% | 3.70% | 4.00% | 4.50% | 5.00% |
| 4.00% | 5.50% | 4.15% | 4.38% | 4.75% | 5.13% |
| 4.50% | 5.50% | 4.60% | 4.75% | 5.00% | 5.25% |
| 5.00% | 5.50% | 5.05% | 5.13% | 5.25% | 5.38% |
When the existing rate is 5.00% and the new-funds rate is 5.50%, the blend saves only 0.12%-0.45%, and the flexibility of a full refinance (new term, new amortization, possibly a different lender) may be worth more than that.
Things to Watch Out For
The Rate on the New Funds
Some lenders quote the new-funds rate slightly above their rate for a brand-new mortgage. Asking which rate will be used for the new portion, and comparing it with a new-mortgage quote, shows whether the blend is priced fairly. Checking the lender’s blended figure with the formula above takes a minute.
Payment and Amortization
When the balance goes up, the monthly payment usually rises even if the blended rate is low, because there is more principal to repay. Some lenders recalculate the amortization, others keep the remaining amortization and raise the payment.
Insurance on the Added Funds
Adding funds without a purchase counts as borrowing more against the home. Under the Bank Act, a bank's loan to buy, renovate or improve a home, or a refinance of such a loan, together with any mortgage ranking equal to or ahead of it, can't exceed 80% of the home's value. Mortgage insurance can't lift an ordinary refinance above that limit: under the federal mortgage insurance rules, an insured high-ratio loan has to be for buying the home or for paying off an earlier uninsured low-ratio loan. So if your original mortgage was insured, the new funds on a mid-term increase are uninsured, which can affect the rate the lender offers on them.
A Future Penalty
If you later break the blended mortgage, the penalty is calculated on the blended rate and the full new balance. If rates have fallen below the blended rate by then, an interest rate differential penalty can be large.
Step-by-Step: Getting a Blended Rate Increase
| Step | Action |
|---|---|
| 1 | Contact your current lender and ask about a mid-term increase |
| 2 | Confirm whether it offers a blend to term or only blend and extend |
| 3 | Get the quoted rate for the new-funds portion |
| 4 | Calculate the blended rate yourself to check the lender’s math |
| 5 | Compare the total cost with a full refinance (including any penalty) |
| 6 | Compare the total cost with a separate HELOC for the additional funds |
| 7 | Apply if blending comes out ahead |
| 8 | The lender will usually require an appraisal and standard documentation |
Alternative: A Separate HELOC
Instead of blending, a separate line of credit can carry the additional funds:
| Factor | Blended Mortgage | Separate HELOC |
|---|---|---|
| Rate | Blended fixed rate | Prime + a margin (variable) |
| Payment | Fixed principal + interest | Interest-only minimum |
| Flexibility | Locked until maturity | Repay and reborrow freely |
| Setup cost | Usually no additional fees | $0-500 (some lenders waive) |
| Rate risk | None (blended rate is fixed) | Changes with prime |
| Suits | Certainty and forced repayment | Flexibility, with variable-rate risk |
A HELOC may cost less if prime falls or the additional funds are repaid quickly; a blend gives certainty and a fixed payment. Current HELOC pricing is in HELOC rates in Canada, and the wider choice is compared in HELOC vs refinance.
Related Resources
Sources
The figures and rules on this page come from these sources, last checked against them on September 29, 2026. How we check facts.
- CMHC: CMHC Refinance for Building Secondary Suites
- Financial Consumer Agency of Canada: Breaking your mortgage contract
- Financial Consumer Agency of Canada: Mortgage fees: Prepayment penalties
- Financial Consumer Agency of Canada: Home equity lines of credit
- Justice Laws (Canada): Bank Act
- Justice Laws (Canada): Eligible Mortgage Loan Regulations
- OSFI: Residential mortgage underwriting practices and procedures
- RBC: Variable Rate Mortgage | RBC Royal Bank of Canada