How this calculator works
Enter the amount, contractual annual rate, term, any fee financed with the loan and an optional monthly overpayment. Use the contract or pre-approval rate supplied by the lender.
Calculation method
The model divides the entered annual rate by 12 and uses standard fixed-rate amortisation. Extra payments reduce principal; the final instalment is limited to the balance plus that month’s interest.
Check before using the estimate
The page uses a fixed-rate monthly amortisation scenario. Compare products with the lender’s disclosed all-in annualised cost, daily-interest method, fees, early-repayment terms and arrears conditions.
Worked example
Defaults: principal ¥100,000, annual rate 5.00%, 36 periods, no fee, no overpayment.
| Item | Calculation | Amount |
|---|---|---|
| Monthly rate | 5.00% ÷ 12 | 0.4167% |
| Monthly payment | ¥100,000 × 0.4167% × (1+0.4167%)^36 ÷ ((1+0.4167%)^36 − 1) | ¥2,997.09 |
| Total paid | ¥2,997.09 × 36 | ≈ ¥107,895 |
| Total interest | ¥107,895 − ¥100,000 | ≈ ¥7,895 |
| 0% rate verification (¥1,200 / 12 periods) | Payment = principal ÷ periods | ¥100, no interest |
The 5.00% default is a planning starting point, not a market quote; replace it with the contract or pre-approval rate.
Input variations
| Change | Monthly payment | Total interest | vs default |
|---|---|---|---|
| Add ¥2,000 fee financed into principal | ¥3,057 | ≈ ¥8,057 | Principal becomes ¥102,000 |
| Add ¥500 monthly overpayment | ¥3,497 | Saves ≈ ¥1,500 | Term 36 → about 31 months |
| Rate 5% → 8% | ¥3,134 | ≈ ¥12,800 | Payment +¥137, interest +¥4,905 |
A financed fee increases both payment and total interest; overpayments shorten the term without reducing the payment; a rate rise hits total interest harder than the monthly payment.
Differences from official documents
Differences from actual bank repayment arise because: banks may accrue interest daily (30/360 or actual-day count), so monthly amortisation approximations differ from daily-interest results; the contract-disclosed "all-in annualised cost" or "annualised interest rate" includes handling, guarantee and insurance fees, while this tool computes payment on the nominal annual rate; prepayment may attract a penalty (remaining balance × 1–5%, or contractually waived); floating-rate loans reprice and the payment changes, while this tool does fixed-rate scenarios only; arrears accrue penalty interest daily.
Thresholds and limits
Principal ¥0–¥100,000,000; annual rate 0%–100% (required, blank produces no result); term 1–600 months; financed fee ¥0–¥10,000,000; overpayment ¥0–¥10,000,000. No default rate — personal loans have no nationwide quote, so the user must enter a contract or pre-approval rate.
Documents to check
Loan contract (principal, rate, term, repayment method, fees, prepayment terms, penalty terms); repayment schedule provided by the lender or in their app; monthly repayment notification (verify actual debit date and amount); prepayment application confirmation and fee schedule; personal credit report (verify loan balance and current status); product information sheet or promotional leaflet (verify disclosed annualised rate).
Contract rate, financed fees and all-in cost are different
The fixed payment answers only the entered principal, nominal rate and term.
Financed fees increase balance and interest
Cash-paid or withheld fees should not be entered as financed principal.
Extra payment does not replace contract terms
Actual daily interest, allocation, penalties and prepayment conditions can differ.