How Credit Card Interest Works
Last updated: June 2026
How the charge is calculated
Credit card interest is quoted as an APR, but it's applied monthly. Divide the APR by 12 to get the monthly rate, then apply it to your balance. At 22% APR, the monthly rate is about 1.83%. On a $5,000 balance that's roughly $92 of interest in a single month — before you've bought anything new.
Crucially, if you don't pay the balance in full, interest is added to it, and next month's interest is charged on that larger amount. That's compounding working against you.
Why minimum payments trap you
A minimum payment is mostly interest plus a sliver of principal. On that $5,000 balance at 22%, paying only the minimum can take well over a decade and more than double what you originally owed. The balance barely moves because almost all of each payment is eaten by interest.
A worked example
Take the same $5,000 at 22% APR:
- Paying $150/month clears it in about 50 months with roughly $2,200 in interest.
- Paying $250/month clears it in about 24 months with roughly $1,150 in interest.
Raising the payment by $100 nearly halves both the time and the interest, because far more of each payment now attacks the principal.
How to pay less interest
- Pay in full each month when possible — most cards charge no interest if you do.
- Pay more than the minimum — every extra dollar goes straight to principal.
- Target the highest APR first if you carry several cards (the avalanche method).
- Consider a 0% balance transfer — but mind the transfer fee and the date the promo rate ends.
Use the calculator
Put these ideas to work with the Credit Card Payoff Calculator. You can also browse all MoneyCalcKit calculators or read the calculator methodology for formulas and assumptions.
Frequently asked questions
How is credit card interest calculated?
The APR is divided by 12 to get a monthly rate, which is applied to your balance. Unpaid interest is added to the balance, so it compounds.
Why does paying the minimum take so long?
Minimum payments are mostly interest with a tiny bit of principal, so the balance barely falls. Paying a fixed higher amount clears the card far faster.
Does paying in full avoid interest?
On most cards, paying the statement balance in full each month means no interest is charged on purchases, thanks to the grace period.