Variable-rate mortgages: why a rate jump hits borrowers unequally
On a variable-rate mortgage whose payment is reset, a rise in the rate feeds straight into the amount paid each month; the size of that extra cost depends mostly on how large the jump is, far less on the remaining term.
How much does a rate jump add to a variable-rate mortgage payment? A calculator for the extra monthly cost, and how the risk depends on the loan’s structure.
“Variable rate” instantly signals risk: the payment that spirals when rates climb. The reality is more structured. A variable-rate loan does not respond uniformly to a rise, and depending on how it is built, the same rate move can change everything about the monthly payment — or nothing at all. The calculator below quantifies the first case; what follows explains why the second exists.
What a rate jump adds to your monthly payment
Enter your outstanding balance, remaining term and current rate, then a hypothetical rate jump. The tool shows the extra monthly cost — and how it scales with the size of the jump. It assumes a loan whose payment is recalculated at reset; a constant-payment loan would instead absorb the shock by extending its term.
Conditional arithmetic, non-predictive · the tool makes no assumption about future rate moves · assumptions entered by the user · monthly payment of an amortising variable-rate loan repriced on the outstanding balance · Eco3min — educational tool, neither advice nor a recommendation.
What the calculator computes, and what it assumes
The tool compares two monthly payments: the one at the current rate, and the one after the rate jump you enter. Both are computed on the outstanding balance over the remaining term, using the standard constant-payment amortisation formula. The gap between them is the extra monthly cost, reported per month and per year.
One assumption is decisive: the calculator assumes a loan whose payment is recalculated at each reset. That is the case that produces an immediate increase in the amount paid each month. A loan built differently — payment held constant, term left to lengthen — would absorb the same shock without touching the monthly budget. That distinction is taken up below.
Why the extra cost is almost proportional to the jump
On an outstanding balance of €200,000 at 3.5% over 20 years, the monthly payment is about €1,160. A jump of +1 point adds roughly €105/month, +2 points about €216/month, +3 points about €331/month. The progression is almost linear: each additional point costs about as much as the one before, only slightly more at large jumps. There is no threshold effect and no dramatic non-linearity — it is the size of the jump, passed through to the outstanding balance, that bites.
The remaining term matters less than one might assume. For the same +2-point jump on €200,000, the extra monthly cost moves from about €182/month with five years left to about €237/month with thirty: a modest range for a term multiplied by six. The variable that drives the extra cost is the rate jump, not the repayment horizon.
Why France is largely shielded from this shock
The mechanism the calculator measures assumes a rate that moves after signing. Yet, according to the ACPR, almost all French home loans are issued at a fixed rate — 98.5% of new lending in 2019, a predominance the supervisor has reaffirmed in its more recent housing-finance reports. For most French borrowers the rate is locked in at the outset: the rate shock described here simply does not reach them. That protection is part of a broader reading of real-estate credit and rate cycles, where the financing structure cushions what the rate environment makes move.
The observation is different elsewhere. In markets where variable-rate structures dominate and the payment is reset — Spain (Euribor-indexed, often reset annually), the United States (adjustable-rate mortgages), the United Kingdom — the same rate jump passes straight into the amount paid each month, exactly as the calculator shows. A borrower’s exposure to a rate rise is therefore first a matter of loan structure and country, before being a matter of the rate level. It is also through this channel that how restrictive monetary policy reaches credit shows up faster in household budgets.
A second cushion applies even to the rare French variable loans: many are capped (a prêt à taux révisable capé, with the rise bounded at +1 to +3 points) or built so that the payment stays constant and the term does the adjusting. In that last case, a rate rise lengthens repayment rather than inflating the payment — the cost shifts in time, not in the monthly budget.
It is often assumed that a variable-rate loan mechanically sees its monthly payment rise the moment rates climb. That is misleading: a large share of variable products keep the payment constant and adjust the term, or cap the rate rise. The correct reading: the extra monthly cost this calculator shows only materialises on a loan whose payment is recalculated at reset — otherwise the shock shifts onto the term, not onto the amount paid each month.
A rate shock is not a universal feature of credit: in France, the fixed-rate structure neutralises it upstream, rather than leaving it to be suffered and then managed.
Frequently asked questions
Does a variable-rate mortgage always see its payment rise when rates climb?
No. It depends on how the loan is built. On a payment-recalculated structure, the rise feeds straight into the amount paid each month. On a constant-payment structure, it is the repayment term that lengthens. And many variable loans are capped, which bounds the possible rate rise. The calculator corresponds to the first case, the one that produces an immediate extra monthly cost.
How much does a payment rise if the rate goes from 3.5% to 5.5%?
On an outstanding balance of €200,000 over 20 years, a +2-point jump adds about €216/month, close to €2,600/year, on a payment-recalculated loan. The order of magnitude scales roughly in proportion to the jump: a +1 point would cost about €105/month, a +3 points about €331/month. The calculator recomputes these amounts for your balance, term and rate.
Does the remaining term change the extra cost of a rate jump much?
Little. For a given rate jump and balance, the extra monthly cost varies modestly with the remaining term: on €200,000 at +2 points, it ranges from about €182/month (five years left) to about €237/month (thirty). It is the size of the jump that drives the extra cost, far more than the repayment horizon.
Are variable-rate mortgages common in France?
No. According to the ACPR, the fixed rate is very largely predominant in new home-loan production (98.5% in 2019, a trend confirmed since). It is a French specificity: in several other European countries and in the United States, variable- or adjustable-rate structures are markedly more present, which leaves borrowers in those markets more directly exposed to the mechanism measured here.
- The extra monthly cost of a rate jump rises roughly in proportion to the size of the jump and depends little on the remaining term.
- This immediate extra cost only materialises on a loan whose payment is recalculated at reset; with a constant payment, the shock shifts onto a longer term.
- In France, the predominance of the fixed rate (ACPR) places most borrowers beyond the reach of this mechanism, unlike markets where variable rates dominate.
Last updated — 1 June 2026
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