Interest-Only Loan Calculator
Interest-only loans keep payments low during an initial period because you pay only the interest each month and none of the principal, so the loan balance never shrinks. At the end of the interest-only period, the full principal is still owed, often arriving as a balloon payment or a reset to higher principal-and-interest payments that can shock an unprepared borrower. These loans are common with HELOCs during the draw period, some mortgages, and certain commercial loans, and they appeal to borrowers who expect rising income, a future lump sum, or who want maximum cash-flow flexibility now. This calculator shows the monthly interest-only payment, the total interest paid over the interest-only period, and the principal still due at the end, so you can plan for the payment reset or the balloon rather than being surprised by it. Enter the loan amount, the interest rate (APR), and the interest-only period in years, and the calculator returns the monthly payment, the total interest over the period, and the principal balance due at the end. The central risk of an interest-only loan is that you build no equity during the interest-only period — your balance stays exactly where it started — so if the asset doesn't appreciate, you've made no progress on principal while taking on the risk of a much higher payment later. Interest-only loans can be useful tools in the right hands, but they require a clear plan for the principal: refinancing, selling the asset, or building the income to handle the higher principal-and-interest payment when the reset arrives. Use this calculator before taking an interest-only loan to see the true cost and the payment cliff at the end, and to stress-test whether the reset payment will be affordable if rates or your circumstances change.
Interest-Only Loan Calculator
Calculate the monthly interest-only payment and the balloon principal due later.
Monthly interest-only payment
$1,875
For 10 years
Total interest over period
$225,000
Principal due at end
$300,000
Interest-only loans keep payments low early on, but the principal doesn't shrink — you owe the full amount when the period ends. Common with HELOCs and some mortgages; plan for the reset.
How to Use This Calculator
- 1Enter the loan amount.
- 2Enter the interest rate (APR).
- 3Enter the interest-only period in years.
- 4Read the monthly payment, total interest, and principal due.
Why It Helps
- ✓Shows the low initial payment clearly.
- ✓Reveals the principal still owed at the end.
- ✓Helps you plan for the payment reset.
- ✓Useful for HELOCs and interest-only mortgages.
About This Calculator
Interest-only loans keep payments low during an initial period because you pay only the interest each month and none of the principal, so the loan balance never shrinks. At the end of the interest-only period, the full principal is still owed, often arriving as a balloon payment or a reset to higher principal-and-interest payments that can shock an unprepared borrower. These loans are common with HELOCs during the draw period, some mortgages, and certain commercial loans, and they appeal to borrowers who expect rising income, a future lump sum, or who want maximum cash-flow flexibility now. This calculator shows the monthly interest-only payment, the total interest paid over the interest-only period, and the principal still due at the end, so you can plan for the payment reset or the balloon rather than being surprised by it. Enter the loan amount, the interest rate (APR), and the interest-only period in years, and the calculator returns the monthly payment, the total interest over the period, and the principal balance due at the end. The central risk of an interest-only loan is that you build no equity during the interest-only period — your balance stays exactly where it started — so if the asset doesn't appreciate, you've made no progress on principal while taking on the risk of a much higher payment later. Interest-only loans can be useful tools in the right hands, but they require a clear plan for the principal: refinancing, selling the asset, or building the income to handle the higher principal-and-interest payment when the reset arrives. Use this calculator before taking an interest-only loan to see the true cost and the payment cliff at the end, and to stress-test whether the reset payment will be affordable if rates or your circumstances change.
Disclaimer: This calculator provides estimates for educational purposes only and does not constitute financial, tax, or investment advice. Results depend on assumptions that may not reflect your actual situation.
Frequently Asked Questions
Why are interest-only payments so low?
Because you pay only the interest each month — none of the principal. The loan balance stays the same until the period ends.
What happens when the interest-only period ends?
You must begin paying principal plus interest, often as a balloon payment or a recast to a higher monthly payment. Plan ahead.
Who uses interest-only loans?
Borrowers expecting rising income or a future lump sum, investors seeking cash-flow flexibility, and some HELOC users during the draw period.
Are interest-only loans risky?
They can be. If your income doesn't rise or you can't refinance, the payment jump at reset can be unaffordable, and you build no equity.
Does the principal ever decrease?
No — during the interest-only period the principal stays constant. You build equity only if the asset appreciates.
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Written by
James MitchellSenior Financial Analyst & Personal Finance Expert
Certified Financial Planner (CFP) • MBA in Finance, University of Chicago Booth School of Business