Mortgage Calculator: Monthly Payment and Amortization

How a mortgage payment is calculated: interest and insurance

A standard repayment loan costs M = P × r × (1 + r)^n ÷ ((1 + r)^n − 1) per month, where r is the annual rate ÷ 12 and n the number of months; the tool adds insurance calculated on the amount borrowed. For 200,000 over 20 years at 3.8% with 0.34% insurance, that is 1,247.65 a month and 99,437 in total borrowing cost.

Formula

Standard loan: M = P × r × (1 + r)^n ÷ ((1 + r)^n − 1), where P is the amount borrowed (price − down payment), r the nominal annual rate ÷ 12 and n the term in months. Monthly insurance is P × insurance rate ÷ 12: it is based on the initial principal and stays fixed for the whole loan.

Example with the default values

A 250,000 property with a 50,000 down payment means 200,000 borrowed over 20 years at 3.8% with 0.34% insurance. Monthly payment: 1,190.99 of loan + 56.67 of insurance = 1,247.65. Total cost: 85,837 of interest + 13,600 of insurance = 99,437. In the first year, 7,482 goes to interest and only 6,810 to principal.

Three repayment types

• Standard: fixed payment; interest dominates early on, principal towards the end.
• Linear: the same share of principal every month (P ÷ n), with interest on a shrinking balance, so the payment falls over time. In the example: 1,523.33 in the first month, 892.64 in the last and 89,917 in total cost, 9,520 less.
• Interest-only (in fine): you pay only interest (690 a month including insurance) and repay the 200,000 in one go at the end; the cost rises to 165,600. This is mostly used for buy-to-let, where interest can be offset against rental income.

What the tool leaves out

Fixed rates only, with no arrangement, guarantee or notary fees, so the result is not an APR. Insurance charged on the outstanding balance would cost less than the figure shown. In France, banks follow the HCSF standard: a debt-to-income ratio of at most 35% including insurance and a term of at most 25 years (27 with a deferral for off-plan purchases or renovation work). This is an estimate, not a loan offer.

Sources and dates: decision of the French High Council for Financial Stability (HCSF) of 29 September 2021 on mortgage lending conditions (Official Journal of 10 October 2021), applicable to loans disbursed from 1 January 2022; that the thresholds still apply in 2026 is not verified against an official text (checked 14/10/2026)

Frequently Asked Questions

Does the calculation include borrower's insurance?

Yes, if you enter an insurance rate, its monthly cost is added to your total monthly repayment.

What is an amortization schedule?

It is a detailed schedule showing monthly or yearly breakdown between principal repayment and interest paid. Essential for knowing your remaining balance.

What is the difference between nominal rate and APR?

The nominal rate is the basic interest rate used to calculate interest. The APR (Annual Percentage Rate) includes all mandatory fees (insurance, origination, guarantee) and represents the true cost of credit.

Is this tool really free?

Yes, all tools on Kristools are 100% free and accessible without registration.

Is my data protected?

Yes. All processing is performed directly and securely inside your browser. No personal data is sent to our servers.