Loan calculator 2026
An amortising loan is repaid in equal monthly instalments made of a shrinking interest part and a growing principal part. This calculator computes the fixed monthly instalment and total interest for a given loan amount, annual rate and repayment term.
- Monthly payment€1,389.58
- Total interest€166,874.36
- Total paid€416,874.36
Over time
Illustration only, not financial advice. Assumes a constant rate and regular intervals; real products vary. Verify with a professional.
How the monthly instalment is worked out
This calculator models a standard amortising loan: a fixed amount borrowed and repaid through equal monthly instalments over a whole number of years. The monthly interest rate, i, is the annual rate you enter divided by twelve — a nominal rate, not an effective annual rate — and the number of instalments, n, is the term in years multiplied by twelve. The instalment is worked out once with the standard annuity formula: payment = principal x i / (1 - (1 + i)^-n). When the rate is 0%, that reduces to the principal split evenly across n months. Every month the calculator then splits the fixed payment into an interest part, charged on the balance still owed, and a principal part that reduces it. The running balance is tracked at full floating-point precision internally; only the figures displayed to you are rounded to two decimal places.
A worked example: a EUR 200,000 loan
Set the loan amount to EUR 200,000, the annual rate to 4%, and the term to 20 years, and the calculator returns a monthly payment of EUR 1,211.96. Over the 240 monthly instalments you pay EUR 290,870.56 in total, of which EUR 200,000 repays the principal and EUR 90,870.56 is interest. You can check the first month by hand: the monthly rate is 4% / 12 = 0.3333%, so the interest on the full balance is EUR 200,000 x 0.003333 = EUR 666.67, leaving EUR 545.29 of that first payment to reduce the principal. Now try changing only the term to 30 years in the widget above: the monthly payment falls, but total interest climbs well above EUR 90,870.56, because the balance takes longer to shrink.
What this calculator assumes
The result rests on several simplifications. The interest rate is treated as fixed for the whole term, even though the slider above lets you test any value from 0% to 15%. Payments are assumed to be equal, monthly, and made on time every month, starting one month after the loan begins. No fees are added or subtracted anywhere in the calculation — no arrangement fee, valuation, mortgage insurance, notary cost, or early-repayment charge — and no tax is applied to the interest or the payment. The term itself must be a whole number of years between 1 and 40; the underlying formula would handle other repayment schedules just as well, but this particular tool only offers the standard equal-instalment case.
Where the estimate stops matching reality
Real loans are rarely this tidy. Many mortgages and personal loans carry a rate that is fixed only for an introductory period and floats afterwards, so the payment shown here for year one may not hold for year fifteen. Lenders typically quote an APR or APRC alongside the nominal rate precisely because it folds in fees this interest-only formula ignores, which is one reason a bank's own illustration usually shows a higher effective cost than this page does. Missed or extra payments, payment holidays, borrowing in a currency other than your income, and any tax treatment of interest where you live all sit outside what this calculator can see — it only ever assumes the schedule you entered is followed exactly.
Reading the result without over-trusting it
Treat the monthly payment and total interest as a mechanical projection, not a quote. The tool is genuinely useful for comparing scenarios against each other — a shorter term against a longer one, a smaller loan against a larger one, one rate against another — because the same simplified formula applies consistently to all of them, so the differences between the numbers stay meaningful even where the absolute figures are not exact. It is less useful as a stand-in for a lender's official offer: that document folds in fees and reflects the true annual cost of credit, figures this calculator was never built to compute.
FAQ
Why might a bank quote a slightly different monthly payment for the same amount, rate and term?
Banks usually publish an APR or APRC alongside the nominal rate, and that figure folds in arrangement fees, valuation costs or mandatory insurance that this calculator does not add. Some lenders also use a different day-count convention for the first, partial month, or round each instalment slightly differently. None of that changes the underlying annuity maths — it just means a real offer layers extra costs and timing details on top of the plain interest-and-principal calculation shown here.
Does paying extra each month reduce the total interest shown here?
No — this calculator does not model extra or overpayments; it always assumes exactly the calculated instalment is paid, every month, for the full term. You can approximate the effect of overpaying by re-running the calculator with a shorter term or a smaller loan amount and comparing the totals. In reality, extra payments reduce the balance faster than this schedule does, so less interest accrues on it than the figures above show.
Why does the split between interest and principal in each payment change over the term?
Each month's interest charge is the outstanding balance multiplied by the monthly rate, so it is largest at the very start, when the balance is largest. Because the total payment stays fixed, whatever is left over after covering that interest goes toward principal — and that leftover grows every month as the balance, and therefore the interest charge, shrinks. Late in the term, almost all of each payment reduces principal.
Why does stretching the term from 20 to 30 years lower the monthly payment but raise total interest?
A longer term spreads the same principal over more instalments, so each one is smaller. But the balance also comes down more slowly, which means more months of interest accruing on a larger remaining balance. The lower monthly payment and the higher total interest are two sides of the same change: more months of paying means a larger share of every euro paid is interest rather than principal.