How the mortgage comparator works
This free tool compares up to ten mortgages at once, calculated with the French amortisation system, which is what the calculator implements. Enter the loan amount, the term in years, the nominal interest rate and the costs, and you instantly get the monthly payment, the total interest, the estimated APR and the overall cost of each option to decide which suits you.
What is the French amortisation system?
In the French system you pay a constant monthly payment for the whole life of the loan. What changes month to month is its composition: at first most of the payment is interest and a small part repays principal; over time the proportion reverses and you repay more each time. This calculator implements that system (constant payment).
The monthly payment is calculated with this formula, where C is the principal, i the monthly interest rate (the annual nominal rate divided by 12) and n the number of months:
If the interest rate is 0 %, the payment is simply the principal divided by the number of months.
What is the APR and why does it differ from the nominal rate?
The nominal rate (TIN) is the percentage the bank applies to the outstanding capital. The APR (TAE) is a more complete measure: it reflects the real annual cost of the loan because it incorporates the monthly compounding of interest and the associated costs (fees, certain tied insurance, countable upfront costs).
The APR is normally equal to or higher than the nominal rate, and it is the figure that truly lets you compare two mortgages: two loans with the same nominal rate can have very different APRs if one carries more costs. This comparator computes the APR by solving the internal rate of return (IRR) of the real monthly flows — payments plus the costs you mark as countable — set equal to the net capital received.
Upfront costs and recurring costs
The tool distinguishes several types of cost so the comparison is realistic:
- Upfront costs counted in the APR: the arrangement fee (which by law covers study, processing and granting), the valuation when it is necessary to obtain the loan and other tied costs that the legislation includes in the APR calculation.
- Other upfront costs: costs you pay once but that do not count towards the APR (for example, voluntary costs not required by the bank). If the valuation is a condition for the loan, it goes in the previous box.
- Recurring costs: home insurance, life insurance, service charge, etc. You can set the amount, whether it is monthly or yearly, and decide individually whether each one counts towards the APR.
Metrics it calculates
- Payment / mo: the constant mortgage payment, without extras.
- Average recurring payment: the payment plus the monthly proration of the recurring costs.
- Average cost / mo: adds the proration of the upfront costs over the whole life of the loan.
- Estimated APR: equivalent real annual cost.
- Total interest and total mortgage payments: how much interest you pay and the sum of all the payments.
- Overall cost: mortgage + recurring costs + upfront costs over the whole life of the loan. It is the figure the verdict uses to point out the cheapest option.
Frequently asked questions
Are the results accurate?
The formulas are the standard ones for the French system and for the APR computed by IRR. Even so, it is an indicative estimate: your bank may apply different rounding, fees or tied products. The bank's FEIN sets out the binding offer and the figures calculated under its own conditions and assumptions; on variable-rate mortgages the APR, the payments and the effective cost can change.
Does it work for variable-rate mortgages?
The comparator assumes a fixed interest rate for the whole life of the loan. For variable-rate mortgages (Euribor + margin) you can use it as an approximation by entering a hypothetical rate or the one stated in your contractual documentation, but the real payment will change at each review.
Does it store my data?
All calculations run in your browser and no figure is sent to any server. So you do not lose your work on reload, the data you enter (amount, term, rate, costs and items) and your theme preference are saved in your own browser's local storage: it never leaves your device and you can clear it whenever you like with the "Start over" button.
Notice: this calculator is for information and educational purposes. It is not financial advice or a loan offer. Before taking out a mortgage, check the lender's official terms and, if you need it, an independent financial adviser.