semkuInterest only loan calculator
Enter the loan amount, annual interest rate, interest-only period and total term to compare monthly payments and total interest.
Example loan balance by year
| Loan year | Balance at year end ($) | Fully amortizing loan balance at year end ($) |
|---|---|---|
| 1 | 300,000.00 | 296,646.82 |
| 2 | 300,000.00 | 293,069.08 |
| 3 | 300,000.00 | 289,251.73 |
| 4 | 300,000.00 | 285,178.72 |
| 5 | 300,000.00 | 280,832.93 |
| 6 | 300,000.00 | 276,196.10 |
| 7 | 300,000.00 | 271,248.73 |
| 8 | 300,000.00 | 265,970.03 |
| 9 | 300,000.00 | 260,337.81 |
| 10 | 300,000.00 | 254,328.38 |
| 11 | 292,436.68 | 247,916.49 |
| 12 | 284,366.83 | 241,075.18 |
| 13 | 275,756.53 | 233,775.70 |
| 14 | 266,569.58 | 225,987.36 |
| 15 | 256,767.36 | 217,677.42 |
| 16 | 246,308.67 | 208,810.95 |
| 17 | 235,149.55 | 199,350.68 |
| 18 | 223,243.07 | 189,256.83 |
| 19 | 210,539.20 | 178,486.98 |
| 20 | 196,984.52 | 166,995.85 |
| 21 | 182,522.07 | 154,735.14 |
| 22 | 167,091.03 | 141,653.30 |
| 23 | 150,626.55 | 127,695.36 |
| 24 | 133,059.42 | 112,802.62 |
| 25 | 114,315.78 | 96,912.49 |
| 26 | 94,316.84 | 79,958.16 |
| 27 | 72,978.54 | 61,868.38 |
| 28 | 50,211.17 | 42,567.08 |
| 29 | 25,919.03 | 21,973.15 |
| 30 | 0.00 | 0.00 |
Calculation rules
The calculation assumes monthly payments and monthly compounding, using the annual interest rate divided by 12 as the monthly rate. During the interest-only period, payments cover interest and do not reduce the principal. The remaining principal is then repaid in equal monthly payments over the remaining term.
Taxes, insurance, PMI and fees are not included.
The interest rate is assumed to stay fixed for the full term. Adjustable-rate mortgages (ARMs) are not supported.
Calculations use unrounded payment amounts. Each displayed amount is rounded once to the nearest cent, with trailing zeros kept; ties are rounded away from zero. Total interest is calculated before display rounding, so multiplying a displayed monthly payment by the number of payments can give a different total.
Frequently asked questions
- How is the interest-only monthly payment calculated?
- Multiply the loan amount by the annual interest rate divided by 12. In the example, $300,000 at 6.5% gives an interest-only payment of $1,625.00 per month. The principal stays unchanged during this period.
- Why does the payment rise after the interest-only period?
- The remaining payments must cover both principal and interest over a shorter repayment period. In the example with 10 interest-only years in a 30-year term, the payment becomes $2,236.72 per month, an increase of $611.72.
- What happens if the interest-only period lasts for the full loan term?
- There is no later amortizing period. The full principal is due at maturity in a balloon payment, in addition to the final interest payment. The calculator shows the principal due separately from total interest.
- What does the fully amortizing loan comparison show?
- It uses the same loan amount, fixed rate and total term, with principal-and-interest payments from the start. In the example, the fully amortizing 30-year loan has a monthly payment of $1,896.20 and total interest of $382,633.47. The interest-only example has total interest of $431,812.66.
- Can I use this as an interest only note calculator?
- You can compare a fixed-rate note with the monthly-payment assumptions shown here. If its interest-only period equals its full term, the principal is due at maturity. Check the note's payment terms against these assumptions and your lender's disclosure.
Privacy on this page
Calculations run in your browser. The loan amounts, rates and terms you enter are not sent to the server or saved in browser storage. Reloading the page returns the inputs to their initial state.
To understand how the page is used and to improve the service, this page sends semku’s own usage statistics and automatic error reports. They go only to the dedicated endpoint under semku.com/api/telemetry/v1/. They are not used for advertising or third-party tracking.
The usage statistics include the stage of use (such as starting an operation or requesting a copy), the time it happened and fixed identifiers that distinguish the page and feature. They do not include the loan amounts, rates or terms you enter, the results shown or the text you copy. Inputs are not sent as hashes or as size categories either. The full URL and search terms are not sent.
Operations and sessions are distinguished by randomly generated identifiers. In the browser these exist only in temporary memory and are not written to cookies or browser storage. No identification based on cookies or combined device characteristics is used.
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Separately, when you visit the site, the hosting provider records your IP address, the time of the request and user-agent information about your browser and device in Cloudflare Pages’ standard access logs.
For details, see the privacy policy in Korean.
Calculations run in your browser without sending the financial values you enter to the server or storing them. See “Privacy on this page” for information about access data.