Loan Repayment Calculator (Equal Payment / Equal Principal)

Calculate your monthly payment and total interest from a loan amount, annual interest rate, and repayment term. Supports Japan's two standard mortgage/loan repayment methods: equal payment (元利均等返済) and equal principal (元金均等返済). Everything runs in your browser — the amounts you enter are never sent anywhere.

Everything is calculated in your browser. The amounts you enter are never sent anywhere.

Enter the loan amount, interest rate, and term, then press "Calculate".

How to use

Choose a repayment method: "Equal payment" (a fixed monthly amount) or "Equal principal" (a fixed principal portion each month). Equal payment is the more common default for household budgeting, since the monthly amount never changes.
Enter the loan amount (JPY), the annual interest rate (%), and the term (years and months).
Press "Calculate". You'll see the monthly payment (or, for equal principal, the first and last payments), the total payment, and the total interest.

How it works

How the calculation works

This tool supports the two standard repayment methods used for loans (including mortgages) in Japan: 元利均等返済 ("gan-ri kintou hensai", equal payment) and 元金均等返済 ("gankin kintou hensai", equal principal). If you're not familiar with Japanese loan conventions: these are the same two amortization styles commonly called "fixed-payment" and "fixed-principal" (or "straight-line principal") amortization elsewhere, applied here to a yen-denominated loan with monthly compounding.

Equal payment (fixed monthly payment)

The monthly payment is calculated so that it stays exactly the same for the entire term. Each month, the interest portion is the outstanding balance times the monthly rate, and the principal portion is the payment minus that interest. As the balance goes down over time, the interest portion shrinks and the principal portion grows.

Monthly payment = principal × monthly rate × (1 + monthly rate)^term ÷ ((1 + monthly rate)^term − 1)

(If the interest rate is 0%, the payment is simply the principal divided evenly by the number of months.)

The total payment is the rounded monthly payment (to the nearest yen) multiplied by the number of months. Total interest is the total payment minus the principal.

Equal principal (fixed principal portion)

The principal portion (loan amount ÷ number of months) stays the same every month, and interest is calculated on the remaining balance each month. Because the principal portion is fixed while the balance shrinks, the total monthly payment is highest on the first payment and decreases by a fixed step each month, reaching its lowest point on the last payment.

Total interest is the sum of each month's interest (balance × monthly rate) over the whole term. Total payment is the principal plus total interest.

Which one is "better"?

For the same loan amount, interest rate, and term, equal principal repayment results in less total interest than equal payment, because the balance (and therefore the interest charged on it) shrinks faster. However, the first payment under equal principal is higher than any payment under equal payment, so the initial monthly burden is heavier. The right choice depends on whether you prioritize a lower total cost or a lower, predictable payment from day one.

Rounding

Displayed amounts are rounded to the nearest yen. Intermediate values (balances, per-period interest) are not rounded during the calculation — only the final figures shown to you are. Some financial institutions round every individual installment and adjust the final payment to correct for accumulated rounding; this tool does not replicate that level of detail, since it is an estimation tool rather than a contract-grade amortization schedule.

Out of scope

This tool does not account for bonus-linked payments (common in Japan, where borrowers make an extra lump-sum payment twice a year), grace periods before repayment starts, guarantee fees or group credit life insurance premiums bundled into the effective rate, mid-term rate changes, or early repayment simulations. For an actual loan, check the lender's own quote or simulation.

This tool provides a general-purpose estimate. For decisions about an actual loan, please confirm the terms with your financial institution or a qualified advisor.

FAQ

Are the amounts I enter sent anywhere?

No. All calculations happen entirely in your browser, and no data is ever transmitted externally.

Which is better, equal payment or equal principal repayment?

For the same loan amount, interest rate, and term, equal principal repayment results in less total interest. However, its first payment is higher than any payment under equal payment repayment, so it puts more pressure on your budget right after the loan starts. Choose based on whether minimizing total cost or having a level, predictable monthly payment matters more to you.

Does this include bonus payments or guarantee fees?

No. This tool is an estimate based only on the loan amount, annual interest rate, and term. Actual terms — including bonus-linked payments, grace periods, guarantee fees, and group credit life insurance premiums — vary by lender, so check your lender's own simulation for an exact figure.

How are the displayed amounts rounded?

Results are rounded to the nearest yen. This tool does not replicate the contract-grade practice some lenders use of rounding every individual installment and adjusting the final payment to correct for accumulated rounding. Treat the figures as estimates.

Is the term entered in months or years?

You enter the term as years and months separately, and the tool converts it to a total number of months internally (for example, 10 years becomes 120 months). You can enter anywhere from 1 month up to 600 months (50 years).