Credit Card Interest Calculator
See what your credit card balance really costs.
All calculations happen locally in your browser — nothing is uploaded, stored or tracked.
Enter balance and APR
Your card's current numbers.
Enter your payment
Fixed monthly amount.
Read the result
Monthly interest, payoff time and total cost.
What Is Credit Card Interest?
Credit card interest is charged on balances carried past the grace period, typically daily at the APR divided by 365. The calculator shows the monthly interest charge on your balance and — the part most people miss — how long the balance takes to pay off at a given monthly payment, and the total interest.
Because interest compounds daily, paying only minimums can keep a balance alive for decades. The calculator makes that timeline explicit.
The Method
The simulation charges daily interest on the average daily balance and applies your monthly payment, tracking the balance until payoff.
Your data never leaves your device.
Every calculation on this site runs in your browser using vanilla JavaScript. Nothing is uploaded, stored or tracked.
- 100% local, client-side calculations
- No data stored on any server
- No tracking, no analytics, no ads scripts
- Works offline once loaded
Frequently Asked Questions
How is credit card interest calculated?
At the daily rate (APR ÷ 365) on the carried balance. If you pay the full statement balance each month, no interest accrues.
How long will it take to pay off my card?
The calculator simulates your payment until the balance reaches zero — it depends heavily on the payment amount.
Why does paying the minimum take so long?
The minimum payment barely exceeds the monthly interest, so the principal shrinks slowly — often taking 20+ years.
What is a grace period?
The ~21–25 days between statement and due date. Pay in full within it and no interest is charged.
Does the calculator include fees?
No — it models interest only. Late fees and balance-transfer fees are separate.