How this calculator works
Both rates are amortised on the same loan and term, and the calculator adds up the interest each one costs over the period you set, usually the length of the fixed term. It reports the monthly repayment on each rate and the interest difference over the horizon, then names the cheaper option. Because it holds both rates steady, it compares today's rates rather than guessing where a variable rate will go.
A worked comparison
On a €300,000 loan over 30 years, a 3.5% fixed rate costs about €1,347 a month while a 4.15% variable costs about €1,458, roughly €111 more each month. Across a five-year fixed term the variable rate costs about €9,574 more in interest, so the fixed rate is the cheaper choice at these rates. Raise the variable rate to stress-test a rise, or lower it below the fixed rate to see the point where variable wins.
Certainty versus flexibility
- Fixed — a locked repayment and protection from rate rises, at the cost of a possible break fee if you leave early.
- Variable — freedom to overpay and switch without penalty, but the rate can rise at any time.
- Horizon — the shorter the period, the less a future rate change matters to the comparison.
A note on accuracy
This holds both rates constant, so it does not predict variable-rate changes or model a break fee, and it assumes the same term on each. Compare current fixed and variable rates through the CCPC mortgage comparison, and see our methodology for the formulas.