Blend and Extend Mortgage: How the Rate Is Calculated (With Calculator)

If you locked in a low mortgage rate years ago and now want to borrow more — or break your term early — a blend-and-extend can be the quiet middle path between keeping your old rate and paying a penalty to refinance. It is especially common in Canada and with portfolio lenders, and the whole thing turns on one number: the blended rate.

A blend-and-extend mortgage combines your existing rate with the lender's current rate into a single weighted-average rate, then extends (resets) your term. You avoid a prepayment penalty and keep part of your old low rate, but you give up the chance to shop the open market. The blended rate is weighted by how much of your balance sits at the old rate versus the new money and remaining time.

Model the blended rate on your first and second components here:

How the Blended Rate Works

There are two flavours, and they weight the rates differently:

• Blend to term: your old rate is blended with the current rate for your remaining term. Simpler, and usually the cheaper blend.
• Blend and extend: you reset to a fresh full term (say a new 5-year), so more of the balance is exposed to today's rate for longer. The blended rate sits closer to the current market rate.

Blended Rate = (Old Balance × Old Rate + New Money × Current Rate) / Total Balance

Worked Example

You owe $300,000 at 3.0% with 2 years left, and you want to borrow an extra $100,000. Today's rate is 6.0%.

Blended rate = $15,000 ÷ $400,000 = 3.75%. You access $100,000 at an effective 3.75% blend instead of taking the whole $400,000 at 6% — and you skip any penalty to break the original term.

When Blend and Extend Makes Sense

• You have a below-market rate worth preserving on a large balance.
• You need additional funds (renovation, another property) but not a full new mortgage.
• Breaking your term would trigger a prepayment penalty that a blend avoids.
• Rates have risen since you locked, so keeping part of your old rate has real value.

When to Skip It

• Current rates are at or below your existing rate — just refinance normally.
• The lender's blend uses an inflated current rate — a competitor's refinance may beat it even after penalties.
• You are near the end of your term anyway; waiting costs little.

Whatever the lender quotes, verify it yourself. The blend is just a weighted average interest rate, and if the number they give you does not match your own math, ask why.

Frequently Asked Questions

What is a blend and extend mortgage?

A blend-and-extend mortgage combines your existing mortgage rate with the lender's current rate into one blended rate and resets your term to a new full length. It lets you borrow more or change your mortgage without paying a prepayment penalty, while keeping part of your original rate.

How is a blend and extend rate calculated?

Multiply your existing balance by your old rate and your new borrowing by the current rate, add the two, and divide by the total balance. The result is a weighted-average (blended) rate that sits between your old rate and today's rate, weighted by the size of each portion.

Is blend and extend cheaper than refinancing?

Sometimes. A blend avoids prepayment penalties and preserves part of a low rate, which can beat a full refinance when rates have risen. But lenders control the "current rate" in the blend, so always compare the blended result against an outside refinance including any penalty before deciding.

What's the difference between blend-to-term and blend-and-extend?

Blend-to-term blends your old rate with the current rate over your remaining term only. Blend-and-extend resets you to a new full term, exposing more of your balance to today's rate for longer — which usually produces a blended rate closer to the current market rate.