Calculate interest-only mortgage payments during the IO period and see the payment jump when amortization begins. Compare total cost to a standard mortgage.
An interest-only mortgage allows you to pay just the interest on your loan for an initial period — typically 5 to 10 years — resulting in lower monthly payments during that phase. Once the interest-only (IO) period ends, the loan converts to a fully amortizing mortgage where you begin repaying both principal and interest over the remaining term.
This calculator models both phases so you can see the exact payment during the IO period, the higher payment once amortization kicks in, and the total interest cost over the life of the loan. You can also compare the IO mortgage against a standard fully amortizing loan to understand the true cost of lower initial payments.
Interest-only mortgages can be useful for borrowers who expect a significant income increase, plan to sell before the IO period ends, or want to redirect cash flow to higher-return investments. However, the payment jump at the end of the IO period can be substantial — sometimes 50% or more.
Lower initial payments sound appealing, but you need to see the full picture before committing. This calculator reveals the payment shock when the IO period ends and how much extra interest you pay compared to a standard mortgage. Armed with these numbers, you can decide whether the short-term cash flow benefit is worth the long-term cost.
Real estate investors frequently use IO mortgages to maximize cash flow on rental properties, while some homeowners use them as a bridge strategy when expecting a future lump sum (bonus, inheritance, or home sale proceeds).
Interest-Only Payment: M_IO = P × (r) where P = principal, r = annual rate / 12 / 100 Amortizing Payment (after IO period): M_amort = P × [r(1+r)^n_rem] / [(1+r)^n_rem − 1] where n_rem = remaining months (total term − IO period) Note: No principal is reduced during the IO period, so the full original balance is amortized over the shorter remaining term.
Result: IO: $2,813/mo → Amortizing: $3,896/mo
A $500,000 loan at 6.75% with a 10-year IO period has interest-only payments of $2,812.50/month. After 120 months, the full $500,000 must be amortized over the remaining 20 years, pushing the payment to $3,895.67/month — a 38% increase. Total interest over 30 years is $599,860, compared to $467,308 on a standard 30-year amortizing mortgage — an extra $132,552.
During the IO period your minimum payment covers only the interest that accrues each month. On a $500,000 loan at 6.75%, that is $2,812.50 per month — significantly less than the $3,243 you would pay on a standard 30-year amortizing mortgage. However, your principal balance remains at $500,000 the entire time. You are essentially renting the money without paying it back.
When the IO period ends, the full original balance must be paid off over the remaining term. If you had a 30-year loan with a 10-year IO period, you now have just 20 years to repay the entire $500,000. This compression drives the payment up significantly. The shorter the remaining term, the higher the amortizing payment.
Savvy borrowers use IO mortgages as a financial tool rather than a way to afford more house. Real estate investors often prefer IO loans because the lower payments maximize rental cash flow. High-income professionals with variable compensation may use IO during lean periods and aggressively prepay during bonus months.
An interest-only mortgage lets you pay only the interest charges for an initial period (typically 5-10 years), keeping your monthly payment low. You are not required to pay any principal during this phase. Once the IO period ends, the loan converts to a standard amortizing mortgage over the remaining term.
No. Since you are only paying interest, your loan balance stays the same throughout the IO period. If you want to reduce the balance, you must make voluntary extra payments toward principal.
The increase depends on the loan amount, rate, and remaining term. On a typical 30-year loan with a 10-year IO period, the amortizing payment can be 30-60% higher because the full balance must be repaid over only 20 years instead of 30.
IO mortgages suit borrowers with irregular income (commission-based), those who plan to sell before the IO period ends, real estate investors maximizing cash flow, or high-net-worth individuals who prefer to invest the payment difference at a higher return. Each of these profiles benefits from lower required payments during the initial years, though a clear exit strategy is essential before the amortization phase begins.
They carry more risk than standard mortgages because you are not building equity through payments, and the payment jump can be substantial. If property values decline, you could owe more than the home is worth. Always have a plan for when the IO period ends.
Most IO mortgages allow voluntary principal payments at any time. This is a smart strategy to gradually reduce your balance and soften the transition to the amortizing phase.
An IO mortgage almost always costs more in total interest because no principal is reduced during the IO phase. The longer the IO period and the higher the rate, the greater the difference. This calculator shows the exact comparison.
Yes, though they are less common than before 2008. They are primarily offered as jumbo loans, portfolio loans, or through credit unions. Qualification requirements are typically stricter, requiring higher credit scores and larger down payments.