Finance category

Mortgage, loan, investing, tax, and money calculators.

Interest-Only Mortgage Calculator

See exactly how an interest-only mortgage works: low payments while interest-only, then a payment jump when full amortization begins. Compare total interest cost against a fully amortizing loan.

Loan amount

Rate

Interest-only years

Total term (years)

Interest-only payment

$2,812

first 10 years

Amortizing payment after IO

$3,625

over remaining 20 years

Payment jump at year 10

+$813

budget shock to plan for

Extra interest vs full amort

+$74,813

cost of the IO period

Reading the number

Interest-only loans keep payments low while you don't pay down principal. The trade-off is a payment jump at the end of the IO period (your full 20-year amortization compresses into less time) and meaningful extra total interest.

Standard fully-amortizing payment over 30 years would be $3,146/mo with total interest of $682,728. Use IO loans when rental income, bonus structure, or a planned sale lines up with the IO period — not as a tool to qualify for more house.

Editorial noteMaintained by EveryCalc - Reviewed June 2026

EveryCalc calculators are designed for fast, practical estimates with transparent inputs and no required account. We use plain formulas, visible assumptions, and related tools so visitors can check the result from more than one angle.

Results are informational only. For financial, tax, legal, medical, construction, or other high-impact decisions, verify the output against primary sources or a qualified professional.

Learn more about our review process on the EveryCalc methodology page.

How this calculator works

What this page estimates

This Interest-Only Mortgage Calculator is built to give a quick, browser-based estimate for interest-only mortgage. See exactly how an interest-only mortgage works: low payments while interest-only, then a payment jump when full amortization begins. Compare total interest cost against a fully amortizing loan. The inputs stay on the page during normal use, and the result should be treated as an estimate for planning, comparison, or education rather than professional advice.

Calculation approach

The calculator applies the standard relationship implied by the inputs, then formats the answer so it can be checked and reused. For finance tools, the most important step is using consistent units, rates, time periods, and assumptions before comparing the result with another calculator or outside quote.

Example workflow

For example, start with a realistic value you already know, change one input at a time, and watch how the answer moves. That makes it easier to tell whether the result is being driven by the main amount, the rate, the time period, or a unit conversion.

Practical checks

Use current, real-world numbers when the result affects money, health, tax, or legal decisions.
Run a low, base, and high case when the inputs are estimates.
Check the related calculators below when the next decision depends on a different assumption.

How to interpret the interest-only mortgage result

Best use

Use the result as a planning number for comparing payments, rates, returns, tax reserves, or cash-flow choices before you request a quote or make a commitment.

Cross-check

Compare the answer with the contract, lender estimate, tax form, brokerage statement, payroll record, or invoice that will control the real-world outcome.

Watch for

Do not rely on a single optimistic rate, return, or fee assumption. Money pages work best when you run low, base, and high cases and keep professional advice separate from the estimate.

This page belongs to the Finance calculator library, so the answer should be read in the context of the decision you are modeling rather than as a universal rule.

Before relying on this interest-only mortgage estimate

Most calculator mistakes come from the inputs, not the arithmetic. Use this short audit before you reuse the answer in a spreadsheet, quote, application, or important conversation.

Confirm source numbers

Match balances, rates, fees, taxes, income, and payment dates against the lender quote, payroll record, tax form, statement, invoice, or contract.

Separate cash flow from total cost

A lower monthly payment can still cost more over time if fees, interest, taxes, or a longer term are hidden in the structure.

Run conservative cases

Test at least one higher-cost or lower-return case before using the output for a purchase, refinance, investment, loan, or tax decision.

Rerun this page when the rate, price, term, fee, tax rule, income, expense, or expected holding period changes.

How to Use

Enter the loan amount, rate, and total term (typically 30 years).
Enter the interest-only period (commonly 5, 7, or 10 years).
Compare the interest-only payment to the amortizing payment that kicks in afterward.
Note the payment jump at reset — this is the key risk to plan around.
Compare total interest paid vs a fully amortizing 30-year loan to size the cost of the IO option.

Frequently Asked Questions

When does interest-only make sense?

When your income or asset value is timed: variable-comp earners with bonus cycles, real estate investors holding for resale, or borrowers expecting a windfall before the IO period ends. It's a poor choice if your only plan is to keep payments low.

How big is the payment jump at reset?

Significant. After a 10-year IO on a 30-year loan, the remaining 20 years must repay 100% of principal — the amortizing payment is materially higher than what a 30-year fully-amortizing loan would have charged from day one.

Can I make principal payments during the IO period?

Most IO loans allow optional principal payments. Doing so reduces both the interest carry and the amortizing payment that kicks in later. Read your note for prepayment restrictions.

What happens if I refinance before the IO period ends?

You pay off the IO loan with the new mortgage and reset the amortization clock. Watch for prepayment penalties — some IO loans have them in the first few years.