Interest-only mortgage calculator
Estimate both phases of a fixed-rate mortgage, using one currency.
Formula
r = annual%/1200; first payment = P×r; later M = P×r/[1−(1+r)^−n]. At 0%, M=P/n.
Interest-only payment/month ≈ (100,000)×(0.005) · Later payment/month ≈ (100,000)×((0.005)+1÷(692.9939624)) · Total interest ≈ (100,000)×((0.005)×(60)+(300)×(0.005)-((692.9939624)-(300))÷(692.9939624))
How to use
- Enter the outstanding principal and annual rate.
- Set months paying only interest, then months repaying principal.
- Compare payments and total interest.
Examples
- 1,200 at 12%: 12/month interest-only, then about 106.62/month over 12 repayment months.
Frequently asked questions
Does the balance fall during the first phase?
No. Only interest is paid; principal remains unchanged.
What happens after that phase?
This model amortizes the full principal over the repayment months you enter.
What is excluded?
Rate changes, taxes, insurance, fees and extra payments. Lender rounding can differ.
Sources
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