Interest-Only Mortgage Calculator
See what you'll pay during the interest-only period, how much your payment jumps when amortization begins, and how the total cost compares to a standard mortgage.
Loan Details
| Interest-Only | Standard | |
|---|---|---|
| IO Phase P&I | — | — |
| Amort Phase P&I | — | — |
| Total Interest | — | — |
| Total P&I | — | — |
| Extra Cost | — | — |
Tax + insurance are shared costs and not shown above.
Show amortization schedule
How Interest-Only Mortgages Work #
An interest-only mortgage splits your loan into two distinct phases. During the initial interest-only period — typically 5, 7, or 10 years — your monthly payment covers only the interest charges on the loan. No principal is repaid during this time, which means your loan balance stays exactly the same as the day you closed. This results in a lower initial payment compared to a standard amortizing mortgage, but it comes with a significant trade-off: you build no equity through your payments during the IO period.
For example, on a $320,000 loan at 6.5% interest, the interest-only payment is approximately $1,733 per month. A standard 30-year fixed payment on the same loan would be about $2,023 per month — roughly $290 more. The IO option saves you $290 per month during the IO phase, but that savings comes at a cost: you are not reducing your principal balance, and every dollar of interest is calculated on the full $320,000 throughout the IO period.
Understanding Payment Shock #
When the interest-only period ends, your mortgage converts to a fully amortizing loan. The full original principal must now be repaid over the remaining term, which is shorter than the original loan term. This causes a substantial increase in your monthly payment — often called "payment shock." The longer the IO period, the greater the shock, because the remaining amortization period is shorter and you must repay the same principal in fewer years.
Using our example: with a 10-year IO period on a 30-year loan at 6.5%, the amortizing payment after year 10 jumps to approximately $2,385 per month — an increase of about $652 over the IO payment, or roughly 38%. If you had a 7-year IO period instead, the remaining 23-year amortization produces a somewhat lower payment jump, because the principal has more time to be repaid. Use the calculator above to model different IO periods and see the exact payment shock for your scenario.
When Interest-Only Makes Sense #
Interest-only mortgages are not inherently bad — they serve specific financial situations well. Real estate investors often use IO loans to minimize cash outflow during a renovation or holding period, planning to sell or refinance before amortization begins. Borrowers with irregular income (such as commission-based salespeople, seasonal business owners, or freelancers) may appreciate the lower required minimum payment, while making voluntary principal payments when cash flow allows.
Some borrowers use IO mortgages strategically: if your mortgage rate is lower than your expected investment returns, you might invest the difference between the IO payment and a standard payment, potentially building more wealth than you would by paying down principal. However, this strategy carries market risk and requires discipline. If home values decline, you could end up owing more than your home is worth — a situation called being "underwater" — because no principal was paid during the IO phase.
Interest-only mortgages are riskier than standard mortgages for most borrowers. Before choosing an IO loan, make sure you have a clear exit strategy (sell, refinance, or the ability to absorb the payment shock) and a solid financial cushion. The lower initial payment should not be the sole reason for choosing this loan type — it should fit within a broader financial plan.
Frequently Asked Questions #
What is an interest-only mortgage?
An interest-only mortgage has two phases: an initial period (typically 5, 7, or 10 years) where you pay only interest, and a remaining period where the loan converts to full principal-and-interest payments. During the IO phase, your balance stays the same because no principal is repaid. After the IO period ends, your monthly payment increases because the full principal must be amortized over the shorter remaining term.
How much does your payment increase after the IO period?
The increase depends on your loan amount, interest rate, and IO period length. On a $320,000 loan at 6.5% with a 10-year IO period, payments jump from about $1,733/mo to approximately $2,385/mo — an increase of roughly $652/mo (38%). Shorter IO periods produce smaller payment shocks because the amortization period is longer.
Interest-only vs standard mortgage: which costs more?
Interest-only mortgages cost significantly more in total interest over the life of the loan. Because no principal is repaid during the IO period, you pay interest on the full balance for those years. On a $320,000 loan at 6.5% with a 10-year IO period, total interest is roughly $100,000 more than a standard 30-year fixed mortgage on the same loan.
Who should consider an interest-only mortgage?
IO mortgages may suit real estate investors, borrowers who expect significantly higher future income, those with irregular income who want lower minimum payments, or borrowers who plan to sell or refinance before the IO period ends. They require discipline and a clear exit strategy to manage the payment shock when amortization begins.
Can you make principal payments during the interest-only period?
Yes. Most IO mortgages allow voluntary principal payments during the IO phase. Making extra payments reduces your balance, which lowers future amortizing payments and reduces total interest. Use our Extra Payment Calculator to model the impact of additional principal payments.
What happens when the interest-only period ends?
The loan automatically converts to a fully amortizing mortgage. Your monthly payment increases to cover both principal and interest over the remaining term. For a 30-year loan with a 10-year IO period, you have 20 years to repay the full principal — resulting in significantly higher monthly payments than if you had 30 years to amortize.
Are interest-only mortgages available for all loan types?
No. IO options are primarily available on conventional jumbo loans and some portfolio loans from banks and credit unions. Government-backed loans (FHA, VA, USDA) do not offer interest-only options. After the 2008 financial crisis, IO availability decreased, but many lenders still offer them to qualified borrowers with strong credit, substantial assets, and at least 20% down.