Credit Card Calculator
$
18.00%
$
Payoff Time2 yrs 8 mo
Total Interest$1,400.00
Total Paid$6,400.00
Carrying a credit card balance means interest compounds on whatever you have not yet repaid, so a fixed monthly payment can take far longer to clear the debt than people expect. This calculator takes a single card’s balance, its APR, and the amount you pay each month, then computes how many months it takes to reach zero and how much of that goes to interest. If your payment cannot even cover one month of interest, it warns you the balance will never fall.
Formula
n = −log(1 − rB/M) / log(1 + r)
- B
- Current card balance
- r
- Monthly rate = APR ÷ 12 ÷ 100
- M
- Fixed monthly payment
- n
- Months to pay off, rounded up to a whole month
How it works
- Enter your current card balance, the annual percentage rate (APR), and the fixed amount you intend to pay each month.
- The calculator first checks whether your payment exceeds one month of interest (balance × APR ÷ 12). If it does not, it flags that the debt can never be paid off at that payment.
- Otherwise it solves the amortization formula for the number of months to reach zero, then reports the payoff time, the total amount paid, and the interest portion of that total.
Worked example
A $5,000 balance at 20% APR paid down at $200 per month.
- Monthly rate r = 20 ÷ 12 ÷ 100 = 0.016667; one month’s interest is 5,000 × 0.016667 = $83.33, well under the $200 payment.
- Solve n = −log(1 − 0.016667 × 5,000 ÷ 200) / log(1.016667) ≈ 32.x, which rounds up to 33 months.
- Total paid: 200 × 33 = $6,600, so interest is 6,600 − 5,000 = $1,600.
The card is paid off in 33 months, with about $1,600 paid in interest on top of the $5,000 balance.
Frequently asked questions
- Why does my payment barely dent the balance?
- Interest is charged each month on the remaining balance, so early payments mostly cover interest and only a little principal. As the balance shrinks the interest portion falls and more of each payment chips away at what you owe.
- What happens if my payment is too small?
- If your monthly payment is less than or equal to one month of interest, the balance grows or holds steady instead of falling. The calculator detects this and warns that the debt cannot be repaid at that payment level.
- How much faster is the payoff if I pay more?
- Raising the payment cuts both the months and the interest, often dramatically, because more goes to principal each month. Try a few payment amounts here to see how a modest increase shortens the timeline.
- Does this assume I stop using the card?
- Yes. The math assumes no new charges are added during repayment. Continuing to spend on the card increases the balance and pushes the payoff date out further than the result shown.