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How the Mortgage Calculator Works — Formula & Guide
This free mortgage calculator uses standard actuarial formulas to compute your monthly repayment, total cost, and full amortization schedule. Understanding the underlying math helps you make better decisions when comparing loan offers from banks across Finland, Sweden, Germany, and the rest of Europe.
Annuity (Fixed-Payment) Formula
The annuity repayment method keeps your monthly installment constant throughout the entire loan term. The payment is calculated using the classic present-value annuity formula:
M = P × [ r(1 + r)ⁿ ] / [ (1 + r)ⁿ − 1 ]
M = Monthly payment (kuukausierä / månatlig betalning / monatliche Rate) P = Principal loan amount (lainapääoma / lånebelopp / Darlehensbetrag) r = Monthly interest rate = Annual rate ÷ 12 ÷ 100 n = Total number of payments = Loan term in years × 12
For example, a €200 000 loan at 4.5% annual interest over 20 years gives a monthly interest rate of r = 0.045 ÷ 12 = 0.00375 and n = 240 payments. Plugging into the formula yields approximately €1 265/month. Over the full term, total repayments come to roughly €303 600, meaning total interest paid is about €103 600 — or 34% of the total cost.
💡 Tip: Even a 0.5% reduction in interest rate on a €200 000 / 20-year loan saves approximately €11 000 in total interest. Always compare the effective annual interest rate (APR / todellinen vuosikorko / effektiv ränta / Effektivzins) rather than just the nominal rate.
Equal Principal (Tasalyhennys / Rak Amortering / Ratentilgung) Formula
With the equal-principal method, the principal repaid each month is constant, while the interest portion decreases as the outstanding balance falls. The formulas are:
Principal per month = P ÷ nInterest (month k) = (P − (k−1) × P/n) × rPayment (month k) = P/n + (P − (k−1) × P/n) × r
The first payment is the highest; each subsequent payment is slightly smaller.
Total interest = r × P × (n + 1) / 2
Because the balance reduces faster with equal-principal loans, total interest paid is generally lower than with an annuity loan at the same rate — but the initial monthly payments are higher. This method is common in Finland (tasalyhennys), Sweden (rak amortering), and Germany (Ratentilgung).
Comparison: Annuity vs. Equal Principal — €200 000 at 4.5% over 20 years
Metric
Annuity
Equal Principal
First monthly payment
€1 265
€1 583
Last monthly payment
€1 265
€838
Total principal repaid
€200 000
€200 000
Total interest paid
≈ €103 600
≈ €90 900
Total cost
≈ €303 600
≈ €290 900
Interest as % of total
≈ 34%
≈ 31%
Understanding the Amortization Schedule
The amortization table (lyhennystaulukko / amorteringsplan / Tilgungsplan / tableau d'amortissement) shows — year by year — how much of each payment goes towards interest versus reducing the principal. In the early years of an annuity loan, the vast majority of each payment is interest. For instance, in month 1 of the example above, €750 is interest and only €515 reduces the principal. By month 200, those proportions have reversed completely.
This "front-loading" of interest is a key reason why making extra repayments early in a mortgage term has such a powerful effect on total cost. Every €1 000 of extra principal repaid in year 1 saves you the compounding interest on that €1 000 for the remaining term.
🇫🇮 Finland — Euribor-linked loans
Most Finnish mortgages are variable-rate loans tied to 3- or 12-month Euribor. The total rate = Euribor + bank margin (typically 0.6–1.5%). OP, Nordea, and S-Pankki are the largest mortgage lenders. Finnish law requires banks to provide a standardised European Standardised Information Sheet (ESIS) before signing.
🇸🇪 Sweden — Bolån & Amorteringskrav
Sweden introduced mandatory amortisation requirements (amorteringskrav) in 2016. Borrowers with a loan-to-value ratio above 50% must amortise at least 1% per year; above 70%, at least 2%. Swedish mortgages are typically annuity loans at variable or fixed rates.
🇩🇪 Germany — Annuitätendarlehen
Germany favours long fixed-rate periods (Zinsbindung) of 5–20 years. The standard product is the Annuitätendarlehen (annuity loan). The effective annual rate (Effektivzins) must be disclosed by law and includes all fees. A Tilgungsplan (amortization schedule) is provided at origination.
🇬🇧 United Kingdom — Repayment Mortgages
UK lenders quote an Annual Percentage Rate (APR). Most residential mortgages are capital-and-interest (repayment) loans with 2- or 5-year fixed initial periods, reverting to the lender's Standard Variable Rate (SVR). The FCA requires a Key Facts Illustration (KFI) for all mortgage products.
Key Mortgage Concepts Explained
Loan-to-Value ratio (LTV / lainasuhde): The ratio of your loan to the property's appraised value. A €160 000 mortgage on a €200 000 home = 80% LTV. Most Finnish banks require at least 10–15% down payment (i.e. maximum 85–90% LTV). Lower LTV typically means a lower margin.
Debt-to-Income ratio (DTI): Lenders assess your total monthly debt payments as a percentage of gross monthly income. In Finland, the Financial Supervisory Authority (Finanssivalvonta) recommends that total housing costs not exceed 45% of net income. This calculator's results help you estimate whether a given loan fits within these guidelines.
Effective Annual Rate (APR / todellinen vuosikorko): Unlike the nominal interest rate, the APR includes origination fees, account maintenance costs, and compounding effects. Always compare APRs when shopping between banks. The formula used in this calculator is based on the nominal annual rate divided by 12 for monthly compounding — if your bank compounds differently, actual results may vary slightly.
Refinancing (lainan kilpailuttaminen): After the initial fixed-rate period ends, or when market rates fall significantly, you may refinance your mortgage to a better rate. Use this calculator to compare your current loan's remaining costs with a new proposed loan — the difference in total interest is the maximum you should pay in refinancing fees to make the switch worthwhile.
📐 Rule of thumb: For every 1 percentage point increase in interest rate, the monthly payment on a €200 000 / 20-year annuity loan increases by approximately €100–110. Use the interest rate slider above to explore how rate changes affect your budget.
Frequently Asked Questions
What is the difference between annuity and equal principal repayment?
With annuity repayment, your monthly payment stays the same for the entire loan term — the split between interest and principal changes over time. With equal principal (tasalyhennys), you repay the same amount of principal each month, so your total payment starts high and gradually decreases as interest charges fall. Equal principal loans cost less in total interest but require higher payments at the start.
How is monthly interest calculated?
The monthly interest charge equals the outstanding loan balance multiplied by the monthly interest rate (annual rate ÷ 12). For a €150 000 balance at 4.8% annual rate: monthly interest = €150 000 × (0.048 ÷ 12) = €150 000 × 0.004 = €600.
Does this calculator account for Euribor changes?
This calculator uses a fixed interest rate for the entire loan term. Real variable-rate loans (like most Finnish mortgages) will have a rate that changes every 3 or 12 months. Use the interest rate input to model different Euribor scenarios — for example, calculate your payment at current Euribor + margin, and again at Euribor + 2% to stress-test your budget.
What other costs should I factor in?
Beyond interest, real mortgage costs include: origination/arrangement fee (järjestelypalkkio), annual account maintenance fee (tilinhoitomaksu), mandatory home insurance (kotivakuutus), possible mortgage insurance (lainasuojavakuutus), property transfer tax (varainsiirtovero, 3–4% in Finland), and notary or registration fees. These are not included in this calculator's output.
How do I use the amortization table?
Click "Show amortization schedule" below the calculator to see a year-by-year breakdown. Each row shows: the annual payment per month, total principal repaid that year, total interest paid that year, and the outstanding balance at year end. This is useful for financial planning, tax reporting (interest may be partially deductible in some countries), and understanding how quickly your equity builds.
This guide is for informational purposes only and does not constitute financial advice. Mortgage terms, regulations, and tax treatment vary by country. Always consult a qualified financial advisor and your lender for personalised guidance. · bestcalculators.eu — Youlearn it Oy