Interest-Only Mortgage Calculator (Realkredit)
Model a mortgage with an interest-only period (afdragsfrihed): see the low payment while you only pay interest and fees, the higher annuity payment once repayment starts, the total cost over the full term, and how the remaining debt develops year by year.
%
%
years
years
Interest and admin margin before tax deductions
- 1
Combined annual rate
4 % + 0.6 % = 4.6 % - 2
Monthly IO payment
2,000,000 × 4.6 % ÷ 12 = 7,667No principal is repaid during the interest-only period — only interest and admin margin.
How does this calculator work?
During an interest-only period you pay L × (rate + admin margin) / 12 per month and the debt stays unchanged; afterwards the loan amortises as an annuity over the remaining years, so the payment steps up. Enter your loan, rate, bidrag and terms to see both payments, the total cost, and the remaining-debt curve.
Formula
How this is calculated
Many mortgages — including Danish realkredit loans — let you start with an interest-only period of up to ten years. During those years you pay only the interest on the full loan plus the lender’s administration margin (bidragssats), so the monthly payment is low but the debt does not shrink. Enter the loan amount, the nominal rate, the admin margin, the total term and the interest-only years to see both phases of the loan.
When the interest-only period ends, the full loan must be repaid over the remaining years, so the payment jumps to a standard annuity calculated on the whole balance across the shorter remaining term — this step-up is the key number to budget for. The calculator shows the payment in both phases, the total amount paid over the life of the loan, and the total cost in interest and fees.
The remaining-debt curve makes the trade-off visible: the balance stays flat during afdragsfrihed, then falls along the annuity path. Payments shown are before tax effects (in Denmark, interest costs are partly deductible) and assume a fixed rate for the whole term; for adjustable-rate loans, re-run the calculation with the new rate at each refixing.
Frequently asked questions
On Danish realkredit loans the mortgage institution charges an annual administration fee — the bidragssats — as a percentage of the outstanding debt, typically 0.3–1.1% depending on loan-to-value and loan type. It is paid on top of the bond interest, so this calculator adds it to the rate in both phases.
Substantially: the entire loan must then be repaid over the remaining term. On a 30-year loan with 10 interest-only years, the whole principal amortises over just 20 years — the payment typically rises by 60–90% depending on the rate. The calculator shows the exact figure for your numbers.
No — it is more expensive over the full term, because you pay interest on the full balance for longer. It improves early cash flow, which can make sense while income is temporarily low or when investing the difference, but the total interest and fees figure shows the real extra cost.
Also known as
TG we-Calculate Editorial Team. (2026). Interest-Only Mortgage Calculator (Realkredit) [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/interest-only-mortgage-calculator
TG we-Calculate Editorial Team. "Interest-Only Mortgage Calculator (Realkredit)." TG we-Calculate. 2026. https://we-calculate.com/calculator/interest-only-mortgage-calculator.
TG we-Calculate Editorial Team, "Interest-Only Mortgage Calculator (Realkredit)," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/interest-only-mortgage-calculator
@misc{wecalculate_interest_only_mortgage_calculator, title = {Interest-Only Mortgage Calculator (Realkredit)}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/interest-only-mortgage-calculator}}, year = {2026}, note = {TG we-Calculate} }
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