Fixed vs Variable Calculator
Compare a fixed rate against a variable one that moves each year, over the deal period, including the balance left at the end.
💼 Are you a real estate agent or broker? Send this calculator to your buyers on your own branded listing page — every enquiry comes straight to your WhatsApp. Create free agent page →A variable rate that starts below a fixed one wins for as long as it stays there and loses once it climbs past. Since nobody knows the path, the useful question is not which will be cheaper but how far rates have to move before fixing pays.
This runs both month by month over the deal period, applying your assumed annual change to the variable rate, and compares total cost including the balance remaining — because a cheaper payment that repaid less principal is not a saving.
How the comparison works
Both loans are run month by month over the deal period. The variable rate steps by your assumed change each year and the payment is recalculated over the remaining term. Each option total cost is everything paid plus the balance still outstanding at the end, so a lower payment that repaid less principal gets no credit for it.
Worked example
On 250,000 over 25 years, comparing five years: a 5.5% fix against a variable starting at 5% and rising half a point a year, so 5.0, 5.5, 6.0, 6.5 and 7.0 across the period. The variable starts cheaper and ends dearer. Over the five years the fixed option costs 315,292 in payments plus remaining balance against 321,020 for the variable, so fixing is 5,728 ahead — the early saving does not survive the later years.
Change the assumption, not the conclusion
The answer is entirely driven by the rate path you enter. Run it at zero change, at half a point, and at a point a year. If fixing wins in all three, the decision is easy; if it flips, you are being paid to take a view on rates, and the premium tells you how much.
Turn a calculation into an enquiry
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Create your free property pageFrequently asked questions
Why include the remaining balance?
Because a cheaper monthly payment that repaid less principal is not a real saving. Comparing payments alone flatters whichever option has the lower payment, which is why total cost has to include what is still owed.
What rate path should I assume?
Test several rather than picking one. The useful output is not a prediction but the size of the gap under each scenario, which tells you what certainty is costing and whether you can absorb the bad case.
Is fixing worth a premium?
It depends on how much slack your budget has. If a two-point rise would be genuinely painful, the premium is buying protection rather than a bet, and paying slightly more for it is rational.