$2,166.67
$2,982.29
$2,528.27
$815.63
37.6
%
$575,750.21
$510,177.95
$65,572.26
$2,166.67
$2,982.29
$2,528.27
$815.63
37.6
%
$575,750.21
$510,177.95
$65,572.26
The Interest-Only Mortgage Calculator helps you figure out what your payments look like on a mortgage that starts off interest-only, then switches to regular payments for the rest of the term. In those first years, you’re just paying the interest—not touching the principal—so your payments start out lower, but you don’t build any equity.
These loans come in two parts. First, there’s the interest-only phase, usually lasting five to ten years. You pay just the interest, which keeps things affordable at the start. When that period ends, the loan shifts gears. Suddenly you’re on the hook for both principal and interest, and you’ve got less time to pay it off. That’s when payments can really jump.
This setup can create a nasty surprise. Take a $400,000 loan at 6.5% interest with a 10-year interest-only period. You’d start out paying about $2,167 a month. But once you hit year eleven and switch to a regular 20-year payment schedule, your monthly payment leaps to around $2,985—a 38% increase. If you’re not ready for that, it can be a real problem.
People usually go for interest-only mortgages when they expect their income to rise a lot, or if they’re investors planning to sell before the bigger payments kick in. Some high-net-worth borrowers use them to free up cash for other investments. For most homebuyers, though, these loans aren’t a great fit. You don’t build equity (unless your home’s value goes up), and you end up paying a lot more interest overall.
After the 2008 financial crisis, lenders tightened the rules on these loans. They need special exemptions now, and banks have to make sure you can actually afford the higher payments when the interest-only period is over—not just the easy part at the beginning.
Interest-Only Payment = Loan Amount × Annual Rate ÷ 12
After the IO period, the full balance is amortized over the remaining term:
Full Payment = P × [r(1+r)n] / [(1+r)n − 1], where n = (Total Term − IO Period) × 12
Payment Increase = Full Payment − IO Payment
Total Interest = (IO Payment × IO months) + (Full Payment × remaining months) − Loan Amount
The interest-only payment shows your cost during the IO period — note that your balance does not decrease during this time. The payment jump shows how much your payment increases when amortization begins. The extra interest vs standard shows the additional cost compared to a standard fully amortizing loan from day one.
Inputs
Results
Payment jumps 38% after IO period. $20K more interest than standard 30-year.
Inputs
Results
Shorter IO period means smaller payment jump but still significant extra interest.
A mortgage where you pay only interest (no principal) for an initial period (typically 5-10 years). After this period, the loan converts to full amortization and your payment increases significantly.
Typically 30-50%, depending on the IO period length, remaining term, and interest rate. On a 10-year IO with 20-year remaining, expect a 35-40% increase.
No — your loan balance stays the same during the IO period. Your only equity comes from home price appreciation or any optional principal payments you choose to make.
High-income borrowers expecting income growth, investors planning to sell before IO ends, or financially sophisticated borrowers who invest the savings elsewhere at higher returns.
Yes, they carry risks: payment shock, no equity building, and negative equity if home values decline. After 2008, regulations require lenders to verify borrowers can afford the fully amortized payment.
Yes. Most IO mortgages allow voluntary principal payments. Any principal paid during the IO period reduces your balance and lowers the fully amortized payment when it kicks in.
Some IO mortgages also have adjustable rates, combining both risks — payment can increase from both rate adjustment and the start of amortization. These loans carry the highest payment shock risk.
They are less common since 2008 but still available, typically from portfolio lenders, credit unions, or jumbo lenders. They require strong qualifications.
Interest payments on mortgages up to $750,000 are tax-deductible. During the IO period, your entire payment is interest and thus potentially deductible (subject to standard/itemized deduction comparison).
Options include refinancing (if equity and credit allow), selling the home, or negotiating a loan modification with the lender. Planning ahead is essential.
Roboculator Team
The Roboculator Team explains calculations, planning tools, and practical formulas in clear language for real-life situations.
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