1. What "fixed" and "variable" mean
A fixed-rate mortgage locks in your interest rate for a set period — often the entire term (US) or 2–10 years (UK, Canada, Australia). Your monthly payment never changes during the fixed period.
A variable-rate mortgage (also called floating or adjustable) moves with market rates. Your payment — or your remaining term, depending on the market — changes when the rate changes. It often starts lower than a fixed rate.
2. The trade-off in plain terms
- Fixed: certainty. You know exactly what you'll pay. No surprises.
- Variable: potentially cheaper. But you carry rate risk — payments can rise.
💡 The real question: is the initial saving on a variable rate worth the risk of future increases? This calculator models it directly.
3. Why variable rates usually start lower
Lenders price fixed rates with a "certainty premium" — they charge more to lock in a rate because they're taking on the risk of rates rising. Variable rates don't have that premium, so they start lower.
Typical difference: 0.5%–1.5% lower for variable. On a $320,000 loan, that's $100–$300/month lower initially — but it comes with risk.
4. Rate-change scenarios
A variable-rate mortgage's cost depends on where rates go:
| Scenario | What happens | Who wins |
|---|---|---|
| Rates fall | Variable payment drops further | Variable rate — by a lot |
| Rates stay flat | Variable stays lower than fixed | Variable rate — modestly |
| Rates rise slowly | Variable creeps up toward fixed | Could go either way |
| Rates rise sharply | Variable exceeds fixed | Fixed rate — clearly |
5. How lenders handle rate changes
Different markets handle variable-rate changes differently:
- US ARMs: the rate is fixed for an initial period (e.g., 5 years), then adjusts annually.
- UK tracker / variable: the rate moves immediately with the Bank of England base rate.
- Canada variable: the rate moves with prime — your payment or term adjusts.
- Australia variable: the rate moves with the RBA cash rate — payment changes.
- India: floating rates are linked to an external benchmark (like the repo rate).
6. When fixed makes more sense
- Rates are expected to rise. Locking in before increases is the classic move.
- Your budget is tight. Certainty matters more when there's less wiggle room.
- You're risk-averse. Peace of mind has real value.
- You plan to stay long-term. Fixed protects against decades of volatility.
7. When variable makes more sense
- Rates are expected to fall. You'll benefit from declines.
- You can handle payment swings. A 2%–3% increase wouldn't strain your budget.
- You'll sell or refinance soon. Rate risk matters less over short periods.
- You want lower initial payments. For cash flow or investment reasons.
- Overpayments are a priority. Variable loans in many markets allow unlimited overpayment without penalty.
8. Common mistakes
- Choosing variable for the lower initial payment only. If you can't afford it if rates rise, it's not the right choice.
- Choosing fixed without comparing. Sometimes the fixed-rate premium is tiny — worth it. Sometimes it's huge.
- Ignoring break fees. Fixed loans often have early repayment charges; variable loans usually don't.
- Not stress-testing. Ask: "Can I afford my payment if the rate goes up 3%?" If no, variable is risky.
- Forgetting that "fixed" isn't forever in some markets. A 5-year fixed in the UK resets to variable after 5 years — often at a much higher rate.
9. How to use this calculator
- Enter the loan amount and term.
- Enter the fixed rate offered by your lender.
- Enter the variable rate and choose a rate-change scenario.
- Set the rate change amount per year (or leave at 0 for "stays flat").
- Add any upfront fees for each option.
- Compare the total cost over the full term.
10. Final thoughts
There's no universally correct answer. Fixed and variable each win in different situations. What matters is matching the choice to your risk tolerance, your expected timeline, and your view on where rates are heading.
If rates rise, fixed looks brilliant. If they fall, variable does. The safest approach for most people: choose fixed if you can't absorb payment increases, and variable if you can — and if the initial savings are substantial.