Calculate an interest-only mortgage payment
Calculating an interest-only mortgage payment starts with principal times the periodic rate during the IO years. The Interest Only Mortgage Calculator needs loan amount, annual rate, interest-only years and amortization years after IO. During IO, payment = balance × periodic rate, and principal stays the same.
After IO, a standard amortizing payment clears the unchanged balance over the remaining years. QuickCalculators reports both payments side by side.
A $400,000 loan at 6% has a monthly IO payment near $2,000 before amortization begins. The post-IO payment is higher because principal repayment starts.
See the interest-only period payment
Seeing the interest-only period payment clarifies the temporary cost of funds. The Interest Only Mortgage Calculator multiplies outstanding principal by the period rate for each IO month. No principal reduction occurs in that phase under a pure IO structure, so equity grows only from property price changes or extra principal payments outside the schedule.
QuickCalculators keeps balance flat across IO rows when a schedule is shown.
IO periods can help short holding plans, but they delay paydown and can raise lifetime interest if the amortizing phase stretches.
See the payment after the interest-only period
Seeing the payment after the interest-only period is the critical stress test. The Interest Only Mortgage Calculator amortizes the full principal over the remaining amort years. If IO ran 5 years and 25 years of amortization follow, the balance is still the original loan when amortization starts.
That produces a sharp payment increase relative to IO. QuickCalculators flags that jump because it is the main risk borrowers miss.
Confirming the amortizing payment against income before signing avoids payment shock when the IO window ends.
Read the disclaimer
QuickCalculators labels Interest Only Mortgage Calculator results as estimates for information only. The Interest Only Mortgage Calculator does not provide lending or financial advice. Rate resets, balloons and lender options may differ from this model.
Correct a common misconception: interest-only means forever low payments
A common misconception is that the interest-only payment lasts for the whole mortgage. It lasts only for the IO years. The Interest Only Mortgage Calculator always shows the later amortizing payment so that temporary low payment is not mistaken for the permanent cost.
Frequently asked questions
What is an interest-only mortgage payment?
An interest-only mortgage payment covers interest on the balance without reducing principal during the IO period. The Interest Only Mortgage Calculator also shows the higher payment that begins when amortization starts.
Why does the payment rise after the IO period?
The payment rises because principal repayment begins while the balance is still near the original amount. QuickCalculators amortizes that balance over the remaining years.
Does principal decline during the interest-only years?
No, under a pure interest-only phase the balance stays flat unless extra principal is paid. The Interest Only Mortgage Calculator models that flat balance during IO.
How is this different from a HELOC?
A HELOC is a revolving line with draw and repayment phases. An interest-only mortgage is typically a closed-end loan with a defined IO window. Use the HELOC Calculator for line-of-credit phasing.
Summarize the Interest Only Mortgage Calculator
The Interest Only Mortgage Calculator computes the IO payment and the later amortizing payment from principal, rate, IO years and amort years. QuickCalculators highlights the payment jump and labels results as estimates, not advice.