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Interest-Only Mortgage Calculator

Compare the initial interest-only payment with the higher payment required to amortize the unchanged principal over the remaining term.

See the payment shock before it happens. Enter the four terms on the loan quote. The interest-only payment, recast payment, and jump update instantly.

Mortgage terms

Fixed-rate planning model. Results update as you type.

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Loan amount Interest rate (%) Interest-only period

years

Total loan term

years

Common IO periods:

Recast rate, date & home value Optional

APR after IO period (%)Use the same rate for a fixed-rate scenario, or enter a what-if reset rate. First payment monthUsed for the transition date and schedule. Home valueOptional. Shows starting LTV and equity that comes from value/down payment, not IO principal paydown.

—Starting LTV

—Equity at IO end if value is unchanged

—First amortizing payment

Interest-only payment—during the IO period Payment after IO period—

—

—Standard P&I payment from day one

—IO-loan total interest

—Extra interest vs. standard P&I

—Balance when IO period ends

Interest only—

Principal + interest—

Principal does not fall during the modeled IO phase. Taxes, insurance, HOA, lender fees, prepayment rules, and ARM index/margin mechanics are not included.

Interest-only vs. standard P&I

Same starting balance, initial APR, and total term. If you enter a different recast APR, only the IO scenario changes after the IO period.

Metric

Interest-only

Standard P&I

Payment during IO period

—

Payment after IO period

—

Balance at IO end

—

Total interest

—

Principal paid during IO years

$0.00

—

View full monthly payment schedule

#	Date	Phase	Payment	Principal	Interest	Balance	Standard balance
Enter a valid mortgage scenario.

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How to use the Interest-Only Mortgage Calculator

Enter the loan amount, rate, interest-only years, and total term. The tool shows the initial interest-only payment and then the payment needed to amortize the unchanged principal over the remaining term.

Important assumptions

The model holds the entered rate constant and assumes no principal reduction during the interest-only period. Real products can have adjustable rates, fees, balloon terms, different reset mechanics, taxes, insurance, or other features.

Practical guide and verification

Use the tool first, then apply these checks to verify inputs, interpret the result, and hand it off without displacing the primary workflow.

Focus on the payment transition, not only the low first payment

During a true interest-only phase the principal normally does not decline, so the later payment must amortize essentially the full balance over fewer remaining years. Compare the payment jump in both dollars and percent, and test whether the later payment still fits the budget before treating the initial payment as affordable.

Separate interest-only and amortizing-phase interest

Total interest is easier to audit when split into interest paid during the IO period and interest paid after amortization begins. The first phase is approximately principal × monthly rate each month under a fixed-rate model; the second phase follows an amortization schedule. Keep both subtotals and the remaining term with the result.

Check the actual loan terms for resets and balloons

Real interest-only products can have adjustable rates, caps, recast dates, balloon payments, fees, prepayment rules, or negative-amortization features. A simplified fixed-rate calculator cannot model contract-specific language. Compare the modeled transition month and balance with the lender disclosure or loan agreement before making a financial decision.

Include housing costs outside principal and interest

Taxes, insurance, HOA charges, mortgage insurance, maintenance, and other ownership costs can materially change the monthly cash requirement. Use the P&I schedule to understand the loan structure, then build a separate all-in housing budget. This calculator is a planning model, not lending, tax, or legal advice.