Credit Card Calculator

How this Credit Card Calculator works

This tool helps you answer two common questions: how long it will take to pay off a credit card balance if you make a fixed monthly payment, and what fixed monthly payment you need to clear the balance in a set number of months. It also shows the total interest paid and a month-by-month breakdown when the payoff period is reasonable.

Key concepts

Balance is the current outstanding amount on the card. APR (annual percentage rate) is the yearly nominal interest rate the card charges. Interest on credit cards is typically compounded monthly for calculation purposes here: we divide the APR by 12 to get a monthly rate and apply that rate to the outstanding balance each month.

Main formulae

Let B be the starting balance, r the monthly rate (APR ÷ 12 as a decimal), P the monthly payment, and n the number of months.

• To calculate the fixed monthly payment required to pay off the balance in n months:

P = r * B / (1 - (1 + r)^-n)

This formula assumes the monthly payment is applied each month and interest is computed before or after depending on contractual terms; this calculator uses the convention of applying the payment once per month and interest computed on the balance before payment of that month’s principal.

• To calculate months n required to pay off the balance given a monthly payment P (when P > r * B):

n = -log(1 - r * B / P) / log(1 + r)

If the monthly payment is less than or equal to the monthly interest (P ≤ r * B), the balance will not decline and the payoff time is infinite.

How totals are derived

Once you have P and n, the total paid is simply P × n. The total interest equals P × n − B. If interest rates or minimum payments change over time in real life, actual totals will differ, but the simplified math here provides a clear baseline for planning.

Practical guidance

Paying at least the full minimum required by the card is essential. However, minimum payments often only cover interest and a small portion of principal, extending payoff for many years. Using this tool to experiment with higher monthly payments shows how small increases in payment drastically reduce payoff time and interest cost.

When to view the amortization table

The calculator will display a month-by-month amortization table when the payoff period is not excessively long (default limit: 600 months). The table shows the interest and principal portions of each payment and the remaining balance after each payment.

Use these calculations for planning and comparison. Results are estimates intended to improve financial clarity and decision-making.