How an interest-only loan works
An interest-only loan splits its life into two phases. In the first, you pay only the interest that accrues on the balance each month — nothing goes toward the principal — so the payment is as low as it can be while the loan is still outstanding. The balance you owe stays frozen at the amount you borrowed. This phase typically runs five to ten years. In the second phase the loan behaves like an ordinary mortgage: each payment now covers both interest and principal, and the balance finally begins to fall. The catch is that the entire principal must be repaid over the shorter time that remains, which is what makes the later payments larger. For the conventional alternative, where principal and interest are blended from day one, see ourmortgage calculator or the more general loan calculator.
Worked example
Take a $300,000 loan at 6% on a 30-year term, with payments covering interest only for the first 5 years. Here is what happens to the payment:
| Step | Amount |
|---|---|
| Loan amount | $300,000 |
| Interest ratefixed, on a 30-year term whose first 5 years are interest-only | 6% |
| Interest-only paymentbalance × the monthly rate — none of it touches the principal | $1,500.00/mo |
| Interest paid during the interest-only years5 years of payments that build no equity — the balance is still $300,000 | $90,000 |
| = Payment once the loan amortizesthe payment shock: $432.90/mo more, because the full balance must be repaid over the remaining 25 years | $1,932.90/mo |
Computed with this calculator's default settings — open the tool above and you'll see the same numbers, then change any input to match your own loan.
The payment shock — and the risks
The defining feature of these loans is the payment shock when the interest-only period ends. Because the full balance is unchanged but the remaining term is shorter, the new amortizing payment is markedly higher than the interest-only payment you had grown used to. If the loan also carries a variable rate, the rate can reset upward at the same moment, compounding the jump. The other quiet cost is equity: during the interest-only years you build none from your payments, since the principal never moves, so every dollar of interest paid in that period buys you no ownership. If property prices stall, you can finish the interest-only phase owing as much as you started. To see exactly how principal would otherwise be chipped away over time, ouramortization calculator lays out the balance month by month.
Who they suit, and the contrast with a standard loan
Interest-only loans can make sense for borrowers who expect their income to grow, who intend to sell or refinance before the interest-only period ends, or who want lower carrying costs in the early years — investors among them. They are riskier for anyone counting on the low payment to last. A standard amortizing loan is the contrast: it costs more each month from the outset, but it pays down principal steadily, builds equity throughout, and carries less interest over its life. The interest-only loan trades certainty later for breathing room now.
Frequently asked questions
What is an interest-only loan?
An interest-only loan lets you pay just the interest for an initial period — often five to ten years — without reducing the principal. Your monthly payment is lower during that window because none of it goes toward the balance you owe. Once the interest-only period ends, the loan converts to a normal repayment schedule and you begin paying down the principal as well.
What is the payment shock when the interest-only period ends?
Payment shock is the sharp jump in your monthly payment that happens the moment the interest-only period finishes. Because the full balance still has to be repaid, but now over a shorter remaining term, the new amortizing payment is meaningfully higher than the interest-only payment was. On a thirty-year loan with a five-year interest-only start, the principal is squeezed into the remaining twenty-five years, which is what drives the increase.
Who are interest-only loans suited to?
They can suit borrowers who expect their income to rise, who plan to sell or refinance before the interest-only period ends, or who have irregular earnings and want flexibility in the early years. Investors sometimes use them to keep carrying costs low. They are riskier for anyone relying on the low payment lasting, since the higher payment and any rate reset can arrive at the same time.
Do you build any equity during the interest-only period?
No. Because your payments cover only interest, the principal stays exactly where it started, so you build no equity from paying down the loan. Any equity gain during that time comes solely from the property rising in value. If prices stay flat or fall, you can reach the end of the interest-only period owing as much as you borrowed.
How does an interest-only loan compare with a standard amortizing loan?
A standard amortizing loan blends interest and principal into every payment from the start, so the balance falls steadily and you build equity throughout. An interest-only loan defers all of that principal repayment, giving lower early payments but higher payments later and more interest paid overall. The amortizing loan costs more each month at first but leaves you owing less sooner.
Disclaimer: This calculator is foreducation and illustration only. It assumes a fixed rate across both phases and a single amortizing schedule once the interest-only period ends; real loans may carry variable rates, balloon payments, or different terms. The figures it produces are not an offer of credit. Nothing here is financial, lending, or investment advice.