Deposit, borrowing and monthly mortgage costs

A first-year financing view

Bilby turns the selected low, expected or high project total into an illustrative borrowing need and monthly interest plus amortisation. It uses your own contribution, lender valuation and interest rate. It is not an annuity repayment schedule or a bank affordability decision, and it does not price household running costs.

Four separate inputs

The scenario selector changes the project-cost input. Your budget target is not the lender valuation.

Need, mortgage capacity and funding gap

Financing need = max(project cost − own contribution, 0). Mortgage capacity = 90% × lender valuation. The illustrative mortgage is the smaller of need and capacity. Any remaining need is shown as additional funding required; it does not disappear because the mortgage is capped.

Loan-to-value is mortgage ÷ lender valuation × 100. Bilby uses 2% annual amortisation above 70% LTV, 1% above 50% through 70%, and 0% at or below 50%. Monthly interest = mortgage × annual rate ÷ 12; monthly amortisation = mortgage × amortisation rate ÷ 12. The higher-interest scenario adds 2 percentage points to your interest input while keeping amortisation unchanged.

Fictional financing example

Select a SEK 5,000,000 project total, contribute SEK 1,000,000, enter a SEK 4,000,000 lender valuation and 4% annual interest. Need is SEK 4,000,000; capacity is SEK 3,600,000; the funding gap is SEK 400,000. LTV is 90%, so annual amortisation is 2%. Monthly interest is SEK 12,000 and amortisation SEK 6,000: SEK 18,000 total. At 6% interest the same model gives SEK 24,000 per month.

At exactly 70% LTV the model uses 1%, and at exactly 50% it uses 0%. A zero valuation gives zero mortgage capacity and no LTV value, rather than implying the remaining need is affordable.

Which lending rule is represented

The implemented rule version is FINANCING_RULES_SE_2026_04. The 90% cap represents a new home purchase from 1 April 2026, not the separate 80% limit for extending an existing mortgage. Lenders still assess valuation, income, expenditure and loan conditions. The model does not decide eligibility for exceptions or guarantee approval. Government of Sweden

Separate amounts remain separate

Choosing a higher budget scenario increases need, but a low valuation can keep the mortgage fixed and enlarge the gap instead. Monthly figures are before tax effects and do not decline month by month as principal is repaid. The construction-credit cost row and mortgage-deed row have their own assumptions; editing this calculator does not synchronise every one of them. Check all three when your lender provides terms. A greater deposit lowers borrowing; changing a cosmetic house option without a budget-price change does not.

Review date and limits

Code and displayed financing controls reviewed 18 October 2026. The enacted 1 April 2026 purchase cap and retained LTV-based amortisation bands were checked against official sources on that date. The higher-interest scenario is Bilby’s +2-point illustration, not a regulatory bank stress test. Swedish Parliament