How long it takes to clear a card balance - minimum payment vs fixed payment.
Each month: interest = balance × APR ÷ 12, then payment − interest reduces principal. Minimum-payment mode recomputes the payment each month as % of balance + interest, with a floor (typical US issuer rule: max(2 % + interest, $25)).
Credit-card debt is the most expensive consumer borrowing on the planet. APRs of 18–25 % are routine, and minimum payments of 2 % of balance + interest leave the principal barely scratched: the famous "minimum-payment trap" can stretch a 5 000 € balance over twenty years and triple the original debt in interest. The arithmetic is non-obvious because the balance and the payment both move every month — interest compounds on what's left, and the minimum payment recomputes each cycle. A calculator that simulates the actual month-by-month dynamics, rather than applying a one-line formula, gives a far more accurate answer than the back-of-envelope "balance / payment" estimate. More importantly, it makes the trap visible: a balance that looks like it will clear in 18 months at the minimum payment in fact takes 14 years.
Each month, in order: 1. Interest accrued = balance × (APR / 12). 2. Payment is determined by the strategy: - Fixed payment: a constant amount you commit to. - Minimum payment (US issuer convention): max(floor, balance × min_pct% + interest). Typical: max($25, 2 % of balance + interest). 3. Principal portion = payment − interest. 4. New balance = balance − principal portion.
Repeat until balance ≤ 0. Total paid is the sum of payments; total interest = total paid − initial balance. The simulation runs up to 60 years (720 months) before declaring the debt non-amortizing — a fixed payment lower than monthly interest never reduces the principal, and the calc surfaces this as an "infinite payoff" warning.
Enter your card balance, the APR, and pick the payment strategy. For fixed payment, set the monthly amount you can commit to. For minimum payment, the calc uses the standard 2 % + interest with a 25 € floor (override if your issuer's rule differs). The result panel shows months to payoff, total paid, total interest, and a balance-decay chart. Watch what happens when you toggle from "minimum" to a 250 € fixed payment on a 5 000 € balance at 19.9 %: months drop from ~22 years to ~2 years, and total interest drops from ~6 100 € to ~600 €.
5 000 € at 19.9 % APR. Minimum payment mode (2 % + interest, $25 floor): - Month 1: interest = 5 000 × 0.0166 = 82.92 €. Min payment = max(25, 100 + 82.92) = 182.92 €. Principal portion = 100 €. New balance = 4 900 €. - Month 24: balance ~3 970 €, interest ~65.86 €, payment ~145.26 €. - Payoff: ~22 years, total paid ~13 800 €, interest ~8 800 € — 176 % of the original principal in interest.
Same balance, fixed 250 €/month: - Month 1: interest 82.92 €, principal 167.08 €. - Payoff: 25 months, total paid ~6 247 €, interest ~1 247 € — 25 % of principal.
The minimum-payment trap is real and the numbers are sobering.
Cash-advance APR is higher. Most cards have 2–3 separate APRs: purchases (the headline rate), balance transfers (often 0 % promotional then jumping to 20 %+), and cash advances (24–28 % from day one with no grace period). The calc uses one APR — make sure it's the rate applicable to the balance you're modeling.
Promotional 0 % windows. Balance-transfer cards offer 12–18 months at 0 % then revert. If you can clear the balance during the promo, the calc with APR = 0 gives the right answer; if not, run the calc twice (0 % for the promo, then post-promo APR for the remainder) and add.
Annual fees and over-limit / late fees. Not modeled. A typical premium card has a 95–550 € annual fee; this is a one-time addition, not part of the amortization. Late and over-limit fees are 25–40 € per occurrence, and many issuers also raise the APR on default (penalty APR ~29 %).
Variable APR. Most consumer cards have variable rates pegged to a benchmark (Fed prime in the US, TEC10 in France). The calc assumes the rate stays constant. In a rising-rate environment your payoff time and total interest both grow.
Compounding frequency. The calc compounds monthly. Some issuers compound daily on average daily balance — the difference is small (about 0.06 %) but real.
Grace period for new purchases. If you pay the full statement balance every cycle, you don't pay interest on new purchases (the grace period). The calc assumes carrying a balance, which removes the grace period entirely — adding a single euro of carry-over kills the grace, so new purchases start accruing interest from the transaction date.
Minimum-payment recompute on payment-due-date. The calc recomputes the minimum each month based on closing balance. Real issuers compute on statement-cycle close; the difference shifts payoff by 0–2 months on long horizons.
Snowball vs avalanche. With multiple cards, the order of payoff matters. The avalanche (highest APR first) minimizes interest; the snowball (smallest balance first) maximizes psychological wins. The calc handles one card at a time — for multi-card strategies, run separately and sum.