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Interest-Only Mortgage Calculator
Compare a lower interest-only payment now against the higher payment — and extra interest — once the loan starts amortizing.
Short answer
An interest-only mortgage lets you pay only the interest for an initial period, so the payment is lower but the balance doesn't fall. When the interest-only period ends, the loan amortizes over the remaining term at a higher payment, and you pay more total interest than a standard loan. Enter your loan and interest-only period below to see both payment stages and the extra cost.
Monthly payment
$2,236.72
Principal + interest
Total interest
$431,813
Total paid
$731,813
Payoff time
30 yr
Interest-only payment: $1,625.00/mo for the first 10 yr, then $2,236.72/mo once the loan amortizes.
Amortization schedule
| Year | Principal | Interest | Balance |
|---|---|---|---|
| 1 | $0 | $19,500 | $300,000 |
| 2 | $0 | $19,500 | $300,000 |
| 3 | $0 | $19,500 | $300,000 |
| 4 | $0 | $19,500 | $300,000 |
| 5 | $0 | $19,500 | $300,000 |
| 6 | $0 | $19,500 | $300,000 |
| 7 | $0 | $19,500 | $300,000 |
| 8 | $0 | $19,500 | $300,000 |
| 9 | $0 | $19,500 | $300,000 |
| 10 | $0 | $19,500 | $300,000 |
| 11 | $7,563 | $19,277 | $292,437 |
| 12 | $8,070 | $18,771 | $284,367 |
| 13 | $8,610 | $18,230 | $275,757 |
| 14 | $9,187 | $17,654 | $266,570 |
| 15 | $9,802 | $17,038 | $256,767 |
| 16 | $10,459 | $16,382 | $246,309 |
| 17 | $11,159 | $15,682 | $235,150 |
| 18 | $11,906 | $14,934 | $223,243 |
| 19 | $12,704 | $14,137 | $210,539 |
| 20 | $13,555 | $13,286 | $196,985 |
| 21 | $14,462 | $12,378 | $182,522 |
| 22 | $15,431 | $11,410 | $167,091 |
| 23 | $16,464 | $10,376 | $150,627 |
| 24 | $17,567 | $9,274 | $133,059 |
| 25 | $18,744 | $8,097 | $114,316 |
| 26 | $19,999 | $6,842 | $94,317 |
| 27 | $21,338 | $5,502 | $72,979 |
| 28 | $22,767 | $4,073 | $50,211 |
| 29 | $24,292 | $2,548 | $25,919 |
| 30 | $25,919 | $922 | $0 |
The trade-off of interest-only payments
During the interest-only period your payment is lower, which frees up cash flow, but you make no progress on the balance. Once the period ends, the full balance must amortize over fewer remaining months, so the payment jumps — and because principal was deferred, total interest is higher. The schedule below makes both stages and the extra cost explicit.
How we calculate this
Every number on this page comes from the standard amortization math a lender uses — the same month-by-month calculation the tool above runs:
- Monthly payment. the fixed principal-and-interest payment is M = P·r ÷ (1 − (1 + r)⁻ⁿ), where P is the loan amount, r is the annual rate ÷ 12, and n is the number of monthly payments. At a 0% rate it's simply P ÷ n.
- Interest each month. the remaining balance times the monthly rate. Because the balance is highest at the start, early payments are mostly interest.
- Principal each month. whatever's left of the payment after interest, plus any extra you pay. Extra dollars go straight to principal and stop accruing interest for the rest of the loan.
Assumptions
- A fixed interest rate for the whole term — adjustable-rate loans (ARMs) reset and are not modeled here.
- Principal and interest only. Property tax, homeowners insurance, PMI, and HOA dues are escrowed on top and not included.
- Educational estimates, not a loan offer or financial advice — your lender's figures govern.
Sources
Last reviewed: July 17, 2026
Frequently asked questions
Related tools
How is mortgage interest calculated?+
Each month, interest is charged on your remaining balance at your annual rate divided by 12. Your fixed monthly payment covers that interest first, and whatever is left pays down principal. Because the balance is highest at the start, early payments are mostly interest; as the balance falls, more of each payment goes to principal. This calculator runs that month-by-month math and shows the full amortization schedule.
How much total interest will I pay on my mortgage?+
It depends on your loan amount, rate, and term. As a rough example, a $300,000 loan at 6.5% over 30 years costs roughly $380,000 in interest — more than the amount borrowed. A shorter term or a lower rate cuts that dramatically, and paying a little extra each month can save tens of thousands. Enter your numbers above to see your exact total interest.
What is an amortization schedule?+
An amortization schedule is a month-by-month (or year-by-year) table showing how each payment splits between interest and principal, and how your balance shrinks over time. It's the clearest way to see how little principal you pay in the early years and how the balance accelerates downward later. This tool generates a full schedule for any loan you enter.
Does paying extra each month really save that much interest?+
Yes — every extra dollar goes straight to principal, so you stop paying interest on it for the rest of the loan. On a 30-year mortgage, even $100–$200 extra a month can cut several years off the term and save tens of thousands in interest. Use the extra-payment field to see your own savings and new payoff date.
What's the difference between the interest rate and APR?+
The interest rate is what's used to calculate your monthly interest. The APR (annual percentage rate) folds in certain loan costs and fees, so it's usually a little higher and is meant to help you compare offers. This calculator works from the interest rate; use APR when comparing lenders' total cost.
How does loan term affect my payment and interest?+
A longer term (like 30 years) lowers your monthly payment but stretches interest over more years, so you pay far more total interest. A shorter term (like 15 years) raises the monthly payment but slashes total interest because the balance is paid down faster. Compare terms above to see the trade-off in both dollars and monthly cash flow.
Estimates for planning only, not financial advice or a loan offer. Principal and interest at a fixed rate; excludes property tax, insurance, PMI, and HOA dues. Your lender's figures govern.