Mortgage calculator
This mortgage calculator uses your loan amount, interest rate and repayment term to work out the monthly annuity payment, the total amount repaid and how much of it is interest. It is handy when comparing bank offers, checking the impact of a longer term, or getting a quick idea of the payment you can afford. Enter three numbers and the result updates instantly.
How a mortgage payment is calculated
A standard mortgage is repaid on an annuity basis — you pay the same monthly amount throughout the fixed-rate period, while the split between interest and principal gradually shifts. At the start more goes to interest, towards the end more to principal. The calculator converts the annual rate to a monthly one and uses the number of monthly payments.
payment = principal × i / (1 − (1 + i)−n), where i = annual rate / 12 and n = years × 12
- Divide the annual rate by 12 to get the monthly interest rate i.
- Multiply the term in years by 12 to get the number of payments n.
- Plug both into the annuity formula to get the monthly payment.
- Multiply the payment by the number of months for the total repaid; subtract the principal to isolate the interest.
Worked example step by step
Take a loan of 3,000,000 CZK, an interest rate of 4.9% p.a. and a term of 30 years.
| Step | Item | Calculation | Amount |
|---|---|---|---|
| 1 | Monthly interest rate i | 4.9% / 12 | 0.40833% |
| 2 | Number of payments n | 30 × 12 | 360 |
| 3 | Monthly payment | 3,000,000 × 0.0040833 / (1 − 1.0040833−360) | 15,922 CZK |
| 4 | Total repaid | 15,921.80 × 360 (from the unrounded payment) | 5,731,849 CZK |
| 5 | Of which interest | 5,731,849 − 3,000,000 | 2,731,849 CZK |
The displayed payment of 15,922 CZK is the rounded value of the exact payment 15,921.80 CZK; for the total the calculator multiplies this unrounded payment (15,921.80 × 360 = 5,731,848.58 → 5,731,849 CZK), so you reproduce the same figure. Over 30 years you would repay roughly 5.73 million CZK, of which nearly 2.73 million is interest alone — almost as much as you originally borrowed.
What affects the result
- Interest rate — even a few tenths of a percent add tens to hundreds of thousands of CZK over the full term.
- Repayment term — a longer term lowers the monthly payment but sharply increases total interest paid.
- Loan amount — both the payment and the interest scale linearly with the principal.
- Rate fixation — once it ends, the rate and payment may change; the calculator assumes a single rate throughout.
- Extra payments — early repayment reduces the principal, shortening the term and the interest; this calculation does not include them.
When the mortgage calculator helps and what to watch out for
The calculator is ideal for quickly comparing offers and gauging the payment you can afford. The result is indicative: it excludes arrangement and servicing fees, mandatory property insurance and any life insurance, valuation, land-registry and other one-off costs. It does not reflect the annual percentage rate of charge (APRC) or a rate change after the fixed period ends. Always verify the actual payment and full costs in the binding offer and pre-contractual information from your bank.
⚠️ Indicative calculation, rates current for 2026. Not a substitute for an accountant or tax advisor — verify important decisions with the Czech Financial Administration.
FAQ
What is the monthly payment on a 3 million CZK mortgage over 30 years at 4.9%?
About 15,922 CZK per month (exactly 15,921.80 CZK). Over the full term you would repay around 5,731,849 CZK, of which roughly 2,731,849 CZK is interest.
What is an annuity payment?
An annuity payment stays the same throughout the fixed-rate period. Only its internal split changes — early on you pay more interest and less principal, and the reverse towards the end.
Does the calculation include insurance and fees?
No. The calculator covers only the loan payment itself. Property insurance, servicing fees, valuation and land-registry charges are not part of the payment and must be added separately.
How does the term affect total interest?
A longer term lowers the monthly payment but extends the interest-accruing period, so you pay considerably more interest overall. A shorter term costs more monthly but less in total.
What happens when the fixed rate ends?
The bank offers a new rate based on current conditions, so the payment may rise or fall. This calculator assumes one rate for the whole term, so treat the result as a model.
Can I repay the mortgage early?
Yes, extra and early repayments are allowed under certain legal conditions. They shorten the term and save interest. This calculation does not account for early repayments.
What is the difference between the interest rate and the APRC?
The interest rate is the price of the borrowed money. The APRC also includes mandatory fees and other loan costs, so it better reflects the true cost. The calculator uses only the interest rate.
How much can I borrow?
It depends on your income, expenses and the property value (LTV). Banks also assess DSTI ratios. The calculator computes the payment, not your borrowing capacity.
Sources & legislation
📅 Last updated: 11 July 2026