Interest-Only Mortgage Calculator
Calculate the interest-only payment, the post-IO payment jump, and total interest versus a standard amortizing loan. Two-phase comparison, free and offline.
Loading tool...
What is Interest-Only Mortgage Calculator?
The Interest-Only Mortgage Calculator splits an IO mortgage into its two phases: the interest-only payment during the IO period, and the higher principal-plus-interest payment that follows, recalculated over the remaining months. It prices a standard amortizing loan on the same term alongside, so the true cost of the IO phase - and the payment shock - is a number, not a surprise.
Key Benefits
- See the exact payment step-up before the bank meeting
- Quantify the total-interest premium of the IO phase
- Compare against a standard loan on identical terms
- Catch impossible IO setups before they reach a lender
- Instant, private, client-side computation
Common Use Cases
- •Evaluating a buy-to-let purchase where cash flow matters most
- •Planning finances before an IO refinance resets the clock
- •Comparing lender offers with different IO periods
- •Teaching borrowers why teaser payments are not free money
How to Compare an Interest-Only Mortgage
- Enter the loan basics: Fill in the loan amount, annual rate, and the total term in years.
- Set the IO period: Choose how many years you pay interest only - the IO and post-IO payments update instantly.
- Compare the totals: Read the standard loan payment and total interest side by side, then weigh the payment relief against the extra cost.
Key Features
- Interest-only monthly payment for the IO phase
- Post-IO payment recalculated over the remaining months - the step-up in plain numbers
- Standard amortizing payment on the full term for a fair comparison
- Total interest for both structures with the exact difference
- Rejects impossible IO periods (equal or longer than the term)
- Pure client-side math - instant, private, free