Mortgage Calculator 2026: Work Out Monthly Instalment, Interest and Residual Debt

Calculate your prefabricated-house financing before the bank does: from total costs, equity, nominal interest rate and repayment, the calculator works out your monthly instalment — and shows honestly what residual debt remains after the fixed-interest period.

Your financing data

Total costs: €450,000

€150,000€1.2m

Equity: €90,000 (20%)

€0€450,000

Fixed nominal interest rate: 3.6% p.a.

2.5%5.5%

Initial repayment rate: 2.5% p.a.

1%5%

Fixed-interest period

Model calculation using the annuity method, excluding commitment interest, special repayments and fees. Your personal interest rate depends on loan-to-value, income and creditworthiness.

Your monthly loan instalment*

€1,830

Loan amount€360,000

Residual debt after 15 years€181,345

Interest paid by then€150,745

Already repaid€178,655

Besides the interest rate, the house price is the second big lever: compare quotes from vetted providers before you finance.

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How to Interpret the Result Correctly

The monthly instalment only shows half the truth of a mortgage — what matters is what remains at the end of the fixed-interest period. A low instalment with 1 percent repayment feels comfortable, but after 15 years leaves a high residual debt that has to be refinanced at the interest rate then applicable. Change the repayment rate in the calculator and watch how the residual debt and interest costs react: it is precisely this interplay that determines the total cost of your own home. As a rule of thumb for 2026 — the instalment should not exceed 35 percent of net household income.

Remember the funding pots: the low-interest KfW programmes 2026 can be built into the financing as a component and noticeably reduce the average interest burden. The current terms are provided by the KfW development bank. How much house you actually need to finance is best clarified in advance with the prefabricated-house cost calculator. The complete roadmap from the equity ratio through the fixed-interest period to the repayment plan with real figures is provided by the guide mortgage financing 2026.

Mortgage Financing: The Interest Environment in 2026

After the swings of previous years, the current interest rates for mortgage financing in 2026 have settled in a corridor of around 3.2 to 4.1 percent — depending on the fixed-interest period, loan-to-value ratio and creditworthiness. For prefabricated-house builders this has two concrete consequences: first, comparing mortgage offers between your house bank, brokers and direct banks pays off more than ever, because the gap between the best and worst offer is often more than 0.4 percentage points. Second, the fixed price of the prefabricated house gains importance: anyone who knows the construction sum and build time with certainty needs less expensive buffer and pays less commitment interest than with a freely planned architect's house.

Key Questions About Mortgage Financing

The most important answers on the monthly instalment, equity, repayment and fixed-interest period for prefabricated-house financing in 2026.

How does the mortgage calculator work out the monthly instalment?

The calculator uses the annuity formula common in Germany: a constant monthly instalment is derived from the loan amount, the fixed nominal interest rate and the initial repayment rate. Within this instalment, the ratio shifts with each payment — the interest portion decreases and the repayment portion increases. In addition, the tool shows what residual debt remains at the end of your fixed-interest period and how much interest you have paid to the bank in total by then.

How much equity should I bring to the mortgage in 2026?

A solid figure is 20 to 30 percent of the total costs — but at least the purchase-related ancillary costs (real estate transfer tax, notary, land register), which banks are reluctant to finance. Anyone contributing 30 percent equity gets noticeably better interest terms in 2026 than with 100-percent financing: depending on the loan-to-value ratio, the difference quickly amounts to 0.5 to 1.0 percentage points — extrapolated over 30 years, a five-figure sum.

Which repayment rate makes sense at the current interest level?

In 2026, financing advisers recommend an initial repayment rate of at least 2 percent, better 3 percent. The reason: at only 1 percent repayment, an annuity loan stretches over well beyond 50 years. Every extra half percentage point of repayment shortens the term by several years and noticeably reduces the total interest costs. Additionally secure special repayment rights of 5 to 10 percent per year — with most banks they cost no surcharge.

Long or short fixed-interest period — what pays off in 2026?

At construction interest rates of 3.2 to 4.1 percent, in 2026 most builders prefer 15 or 20 years of interest-rate security over the classic 10 years. The interest premium for the longer term is moderate, but it removes the risk of an expensive follow-up financing. Good to know: under Section 489 of the German Civil Code (BGB), you may terminate any property loan 10 years after full disbursement with 6 months' notice free of charge — a long term therefore protects you against rate rises while still leaving room for reductions.

Does the calculator replace financing advice?

No — it provides realistic orientation so that you enter the bank meeting well prepared. Your actual interest rate depends on the loan-to-value ratio, income, property value and creditworthiness. Before signing, always obtain several offers: your house bank, broker platforms and the KfW subsidised loans, which can be included as a building block in almost any prefabricated-house financing.