Adjustable Rate vs. Variable Rate Mortgages: How to Pick the Right Float Strategy
Two Canadian borrowers can start with the exact same rate discount off prime and still have radically different experiences once prime moves. The difference comes down to product structure: adjustable-rate mortgages (true variables) change your payment, while fixed-payment variable mortgages change your amortization. Understanding that distinction before you sign avoids surprise payment shocks and frustrating trigger-rate calls later.
Definitions in Plain Language
- Adjustable-rate mortgage (ARM): Your payment resets every time your lender’s prime rate changes. The amortization (how many years are left) remains on schedule.
- Fixed-payment variable: Your payment amount stays the same, even as prime moves. Because the payment is fixed, the amortization stretches or compresses in the background.
Both products “float” with prime, but they distribute the pain differently—either through cashflow or through time.
How Prime Changes Flow Through the Math
Consider a $650,000 balance, 25-year amortization, prime 6.70% with a 1.00% discount (effective rate 5.70%).
- Adjustable payment: $4,090/mo. If prime jumps 0.25%, the payment becomes ~$4,175 to keep amortization true. You feel the change immediately, but you stay on track.
- Fixed-payment variable: Payment stays $4,090/mo. After the hike, interest consumes $3,223 of the payment (up from $3,088), leaving just $867 for principal. Amortization drifts past 30 years unless you add lump sums.
The longer rates stay elevated, the more a fixed-payment variable borrower sacrifices principal reduction.
Trigger Rates & Negative Amortization
Lenders monitor fixed-payment variable mortgages for the trigger rate—the point where your payment no longer covers monthly interest. In our example, that’s roughly prime 7.20%. Hit that level and the lender will demand:
- A higher payment (often dictated by them), or
- A lump sum applied directly to principal, or
- A switch to an adjustable or fixed product.
Translation: payment stability only lasts until rates rise enough to threaten the lender’s capital.
Case Studies: Cashflow vs. Payoff Priorities
Meghan, incorporated consultant
She bills $22K/month but her income is lumpy. Predictable payments help her keep salary/dividend splits tidy, so she chooses a fixed-payment variable—but she pre-schedules $500 monthly prepayments whenever prime rises. That keeps her amortization close to the original 25-year track without shocking cashflow.
Diego, custom builder
He carries multiple projects and wants certainty on when leverage will clear. He picks an adjustable mortgage so every project budget reflects the true payment. When prime moves, he increases the payment the next business day and keeps every build on the same payoff timeline.
Decision Checklist
Ask yourself (and your broker) these questions before you float:
- What matters more—monthly stability or knowing my payoff date?
- How fast can I react to rate changes? If a $120/mo jump would hurt, fixed-payment variable might buy you time.
- Do I have a buffer for trigger rates? Build a savings or LOC cushion covering 1–2% of your balance.
- Am I prepared to prepay proactively? Fixed-payment variables work best when you treat every prime hike as a cue to add $25–$50 to the payment.
- What’s my conversion plan? Confirm the penalty and process to lock into a fixed rate if the Bank of Canada shifts course.
FAQ
Is an adjustable mortgage riskier?
Payment volatility feels risky, but your amortization stays intact. Many risk-averse borrowers prefer this transparency.
Do fixed-payment variables always stretch amortization?
Not when rates fall. In declining-rate environments, the opposite happens—you can shave years off the mortgage without changing payments.
Can I switch from one structure to the other mid-term?
Most lenders will let you convert adjustable ↔ variable or into a fixed term, but you’ll pay a small fee or three months’ interest.
What about business owners with seasonal cashflow?
Pair a fixed-payment variable with a dedicated prepayment routine or a tax/HST reserve account you can tap for lump sums if prime jumps.
How do I budget for prime changes?
Stress-test with ±1.00%. For adjustables, that’s ~$340/mo per point. For fixed-payment variables, aim to prepay 1–2% of the balance annually.
The Bottom Line
- Pick adjustable if amortization certainty and clean project accounting matter most.
- Pick fixed-payment variable if cashflow stability is king, but commit to proactive prepayments so amortization doesn’t balloon.
- Either way, set trigger-rate alerts with your broker, and build a modest reserve so you can react before the lender forces the issue.
Floating your mortgage can still outperform locking in a high fixed rate—but only when you choose the structure that matches your cashflow reality.
