How credit card payoff works
Each month your card adds interest to the balance, then your payment is applied. Only the part of your payment above that month's interest actually reduces what you owe. With a 22.9% APR, a $6,000 balance gathers about $114.50 of interest in the first month (6,000 × 0.229 ÷ 12) — so a $150 payment only knocks about $35.50 off the balance. Next month the balance is slightly lower, so the interest is slightly lower and a little more of the same payment goes to principal. That slow tilt from interest toward principal is why a fixed payment speeds up over time.
The calculator runs that process month by month until the balance hits zero. In “What to pay” mode it works backwards using the loan payment formula M = B × r / (1 − (1 + r)^−n), where B is the balance, r is APR ÷ 12 and n is the number of months. In plain English: the payment has to cover each month's interest and retire the balance in exactly n equal payments.
One rule falls straight out of this: if your payment is not bigger than the first month's interest, the balance never goes down. On the example card, any payment of $114.50 or less means the debt never shrinks, and the calculator shows “never”.
A worked example: $6,000 at 22.9% APR
Suppose you owe $6,000 and stop using the card. A common minimum formula is 1% of the balance plus that month's interest, with a $25 floor, so your first minimum is about $174.50. Paying only the minimum each month — which shrinks as the balance shrinks — takes 20 yr 10 mo and costs about $10,362 in interest, more than the original balance.
Now lock in a fixed payment instead. Here is what different fixed amounts do to the same card, computed with this page's calculator:
| Fixed monthly payment | Time to pay off | Total interest |
|---|---|---|
| $150 | 6 yr 5 mo | $5,435 |
| $175 | 4 yr 9 mo | $3,833 |
| $250 | 2 yr 9 mo | $2,101 |
| $300 | 2 yr 2 mo | $1,630 |
| $400 | 1 yr 6 mo | $1,136 |
Simply keeping the payment at about the first minimum ($175) and never letting it shrink cuts the payoff time to 4 yr 9 mo. If your goal is to be done in two years, “What to pay” mode gives a payment of $313.94 a month, with about $1,535 of total interest.
Why the minimum payment trap is expensive
Issuers typically set the minimum at around 1% of the balance plus that month's interest (with a floor such as $25), though the exact formula varies by card. Because it shrinks as your balance shrinks, minimum-only repayment can stretch a few thousand dollars over a decade or more. A fixed payment — even one only a little above the first minimum — cuts that time dramatically.
Federal rules (Regulation Z, enforced by the CFPB) require your monthly statement to carry a “Minimum Payment Warning”: how long minimum-only payments would take and what they would cost in total. Unless the minimum already pays the balance off within about three years, the statement must also show the monthly payment that clears it in 36 months and how much you would save. Compare that box with this calculator — they should be in the same ballpark, and your statement uses your issuer's exact minimum formula.
Common mistakes
- Letting the payment shrink. Autopay set to “minimum due” quietly lowers your payment every month. Set autopay to a fixed dollar amount instead.
- Paying down the card while still charging on it. New purchases refill the balance, and on most cards carrying a balance means new purchases start collecting interest right away instead of getting a grace period.
- Entering the wrong rate. Use the purchase APR printed on your statement. If part of the balance is a cash advance at a higher APR, the real cost will be higher than this estimate.
- Ignoring the transfer fee. A 0% balance transfer with a 3–5% fee is still a good deal only if you can clear the balance before the promotion ends.
When this calculator doesn't fit
The math assumes one APR, no new charges and no fees. It is less accurate when a 0% promotional period ends partway through, when a store card uses deferred interest (interest from the start of the promotion can be added if the balance isn't paid in full by the deadline), or when one card holds several balances at different rates. Cards also charge interest daily on your average daily balance, so expect small differences from the monthly model used here.
Ways to pay it off faster
- Pay a fixed amount every month instead of the shrinking minimum.
- Ask your issuer for a lower APR — a short phone call sometimes works.
- Stop adding new purchases to the card while you pay it down.
- Send windfalls such as a tax refund or bonus straight to the balance; every dollar stops costing you the card's APR.
- Juggling several cards? Use the debt snowball vs avalanche calculator.
- Not sure how much you can spare? Check your real take-home pay with the paycheck calculator, then see what that same monthly amount could grow to once the card is gone with the compound interest calculator.