Does my balance / amount leave the browser?

No. Balance, APR, monthly payment, and the entire computation happen in JavaScript inside your browser. Nothing is uploaded.

What's the difference between the three methods?

Equal payment fixes the total monthly outflow (interest carved out of it). Equal principal fixes the monthly principal payment; the actual outflow falls as the balance shrinks. Balance-slide changes the required payment in steps depending on the outstanding balance. Japanese credit cards typically use equal payment or balance-slide; the exact wording and applicability depends on the issuer.

Where does the balance-slide table come from?

The defaults match the typical step pattern used by JCB / Saison / Rakuten and similar issuers in Japan: under ¥100k → ¥5,000/mo, ¥100k–¥200k → ¥10,000/mo, and so on in ¥100k buckets. Your exact contract may differ — re-run the simulation against the official table in your member portal for the actual numbers.

What happens if the monthly payment can't cover interest?

The balance never falls. The tool flags 'Balance grows forever' and stops simulating. On a real credit card the situation snowballs because interest and fees keep accruing — increase the monthly amount or pay down extra principal.

What APR should I enter?

Japanese credit-card revolving APRs typically land between 15.0% and 18.0%. Some merchant / co-brand cards offer 9–12%; mainstream issuers cluster around 15%. The exact figure is on your card agreement or in your member portal under '実質年率 (APR)'.

How can I simulate extra principal payments?

There's no built-in extra-payment mode (see loan-calc / mortgage-prepay-jp for mortgage-style prepayment). The simple approach is: subtract the extra payment from the balance, plug the smaller balance back in, and rerun the simulation — then compare the totals.

How accurate is the calculation?

The model is monthly compounding with sub-yen interest truncated. Real issuers do daily compounding and book interest on a fixed cycle, so actual statements may differ by a few hundred to a few thousand yen. The result is plenty accurate for planning; check your statement for the contractual number.

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Credit-card revolving simulator — months to payoff, total interest

Simulate Japanese credit-card revolving (リボ払い) repayments month-by-month from the current balance, fixed monthly payment, and APR. Visualize months-to-payoff, total interest paid, and the principal vs interest split over time. Supports three Japanese-style methods: balance-slide (残高スライド), equal-payment (元利定額), and equal-principal (元金定額). Most card issuers charge 15.0–18.0% APR — keeping the minimum payment low usually grows the balance instead of paying it down, so the tool also lets you compare an extra-payment scenario. Nothing leaves your browser.

financecalculator

How to use

Enter the outstanding balance, APR, and either the monthly payment (equal-payment / balance-slide methods) or the monthly principal (equal-principal method), pick the method, and press Simulate. Interest is computed monthly as balance × APR ÷ 12 with sub-yen amounts truncated (matching how most JP issuers post charges). The summary surfaces months-to-payoff, total paid, total interest, and interest share so you can compare how raising the monthly payment changes both the duration and the total cost. If the monthly payment can't even cover interest the tool warns 'Balance grows forever'. After 50 years (600 months) the simulation cuts off.

FAQ

Does my balance / amount leave the browser?: No. Balance, APR, monthly payment, and the entire computation happen in JavaScript inside your browser. Nothing is uploaded.
What's the difference between the three methods?: Equal payment fixes the total monthly outflow (interest carved out of it). Equal principal fixes the monthly principal payment; the actual outflow falls as the balance shrinks. Balance-slide changes the required payment in steps depending on the outstanding balance. Japanese credit cards typically use equal payment or balance-slide; the exact wording and applicability depends on the issuer.
Where does the balance-slide table come from?: The defaults match the typical step pattern used by JCB / Saison / Rakuten and similar issuers in Japan: under ¥100k → ¥5,000/mo, ¥100k–¥200k → ¥10,000/mo, and so on in ¥100k buckets. Your exact contract may differ — re-run the simulation against the official table in your member portal for the actual numbers.
What happens if the monthly payment can't cover interest?: The balance never falls. The tool flags 'Balance grows forever' and stops simulating. On a real credit card the situation snowballs because interest and fees keep accruing — increase the monthly amount or pay down extra principal.
What APR should I enter?: Japanese credit-card revolving APRs typically land between 15.0% and 18.0%. Some merchant / co-brand cards offer 9–12%; mainstream issuers cluster around 15%. The exact figure is on your card agreement or in your member portal under '実質年率 (APR)'.
How can I simulate extra principal payments?: There's no built-in extra-payment mode (see loan-calc / mortgage-prepay-jp for mortgage-style prepayment). The simple approach is: subtract the extra payment from the balance, plug the smaller balance back in, and rerun the simulation — then compare the totals.
How accurate is the calculation?: The model is monthly compounding with sub-yen interest truncated. Real issuers do daily compounding and book interest on a fixed cycle, so actual statements may differ by a few hundred to a few thousand yen. The result is plenty accurate for planning; check your statement for the contractual number.

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