Skip to content

El Cerebro

Mortgage and housing

Fixed or variable mortgage

Two payments on the same loan, the same capital and the same term: one at the fixed rate you type and one at the Euríbor you type plus the spread you type. The difference between the two payments, multiplied by the months of the term, is the large figure.

With the default values —200.000 €, 25 years, a 2,9 % fixed rate, a 0,6 % spread and the 2,954 % official Euríbor for August 2026— the fixed payment comes out at 938,05 € and the variable one at 1.007,05 €. The difference is 20.698,71 € over the whole term.

What it does

It takes the capital and the term you type, and calculates two payments under the French system. The first, at the fixed rate of the offer. The second, at the rate that comes from adding the spread to the Euríbor. The difference between the two payments, repeated over the months of the term, is the total cost difference: what the variable one would cost more, or less, if the Euríbor stayed at the value you typed for twenty-five years.

That "if" is the important part of the page. The two rates are compared as constants: they are two photographs of the same instant, not two trajectories. A real variable-rate mortgage is reviewed every six or twelve months, and its payment changes over the life of the loan. This account does not project reviews or estimate what will happen. It compares two fixed rates over time, and only one of them comes from a source.

The detail adds the total interest of each option, the Euríbor at which the two payments break even, and how many months the official Euríbor has been above that break-even level since 1999.

Key concepts

  • Euríbor: the reference rate of the mortgage market published by the Banco de España every month through the Boletín Oficial del Estado. The default value on this page is the latest published, and its label carries the month: 2,954 % for August 2026. The full history is on the [Euríbor](/euribor) page.
  • Spread: what the bank adds to the index to set the rate on its offer. It is an assumption that you type: each lender applies its own and it changes with the offer and with the date, so the 0,6 % on the page is an example and not that of any lender.
  • Fixed rate: the one that does not move while the contract lasts, on the terms set out in the deed. The field declares it an assumption because the 2,9 % on the page is not the rate of any specific offer.
  • Break-even Euríbor: the Euríbor value at which the two payments would be equal, which is the fixed rate minus the spread. With 2,9 % and 0,6 %, break-even is at 2,3 %: below that the variable one comes out cheaper, above it it costs more.
  • Constant rates: both rates are assumed not to change over the term. That is what makes the comparison readable, and what the entry repeats, because without that warning a difference of 20.000 € reads like a forecast when it is a comparison between two values fixed today.
  • Total cost: the difference in payment multiplied by the months of the term. It does not include opening fees, insurance, valuation, or the cost of switching one mortgage for another, which are in the contract and not in this account.

Frequently asked questions

How much does one point of Euríbor cost?

With 200.000 € over 25 years, the detail and the sensitivity table give the rest: each point that the variable rate rises brings it to around a thousand euros of difference in the monthly payment. The large figure shows the effect of three points. That is a stress test, not a forecast.

What happens if the Euríbor stays at 2,954 % for twenty-five years?

It is exactly what the page calculates with the default values: a difference of 20.698,71 €. What it does not do is assume that this will be the value. The Euríbor has been above 2,3 % in 141 of the 332 months there have been since January 1999, and that count is a fact about the past, not an expectation about the future.

Is the break-even Euríbor the rate I would be offered?

No. It is the index value at which the two payments in this comparison would be equal, and it comes from subtracting the spread from the fixed rate you typed. It is not a rate that exists in the market, nor an offer: it is the line that separates the two results of the account.

What limits do the fields accept?

The capital runs from a thousand euros to 2.000.000 €, the term from 1 to 40 years, the fixed rate from 0 % to 15 %, the spread from 0 % to 5 % and the Euríbor from −1 % to 15 %. The Euríbor range goes down to negative because the calculation allows for it, and if the result of adding the spread to it came out negative the page would model it at 0 and say so in the detail: a payment with negative interest is not a loan, it is the opposite.

Why does the comparison use constant rates?

Because projecting today's Euríbor twenty-five years ahead would be inventing a series nobody has. With both rates fixed, the account answers a question that does have an answer: how much the difference between these two values costs if they were maintained. The difference between two real Euríbor trajectories cannot be calculated with this module, and the page does not pretend to do it.

What happens with the difference when the figure comes out negative?

It appears with the minus sign and the label says so: with those numbers it is the variable one that is cheaper, not a saving on the fixed one. With an Euríbor below break-even the difference is negative, and so is it with a combined rate clipped to 0.

Is this an offer or a recommendation?

It is neither an offer nor a recommendation: it is an account built on the numbers you type: the fixed rate and the spread are assumptions, and the page does not know what criteria each lender applies, which Euríbor your contract would get, or what deductions might appear in the offer. The decision, and the enquiry to the lender, belong to whoever reads it.

What happens with my data?

The account is resolved in the browser. There is no sign-up, no sending and no storage: the numbers you type stay on the page.

Related calculators

A note to Cerebro

What would you improve?

A member of the team reads it. Tell us what brought you here and what was missing.

The tone of your visit
Between 10 and 2000 characters.0 / 2000

Only if you want an answer.