Credit Card Interest Calculator
Find out exactly how much of your next payment goes to interest versus principal — and what your balance will really cost you over time.
Last updated September 2026 · Reviewed by the CalcMyCard editorial team
A credit card interest calculator shows how much of your next payment goes toward interest versus your actual balance (principal). Enter your balance, APR, and monthly payment below to see the exact split, your total interest cost, and how long payoff will take.
If you carry a balance on a credit card, you're paying interest — and that interest is calculated every single day, not just once a month. Most people only see the final number on their statement, without understanding why so little of their payment seems to move the balance. This calculator breaks that number down so you can see exactly where your money is going.
How this calculator works
Enter three numbers: your current balance, your card's APR (annual percentage rate), and the monthly payment you plan to make. The calculator converts your APR into a monthly interest rate, applies it to your balance, and shows you:
- How much of your next payment is interest versus principal
- Your total interest cost if you keep paying the same amount every month
- How many months (and years) it will take to reach a zero balance
A real example
Say you have a $5,000 balance at 24.99% APR and you pay $150 a month. In the very first month, roughly $104 of that $150 payment is pure interest — leaving only about $46 to actually reduce what you owe. As the balance slowly shrinks, more of each payment starts chipping away at principal, but it takes almost 5 years to reach zero, and you end up paying over $2,600 in interest alone on top of the original $5,000.
Why your balance seems to barely move
Credit cards use compound interest, recalculated against your balance every day (a "daily periodic rate"). The higher your APR and the higher your balance, the bigger the interest chunk of each payment. This is exactly why paying only the minimum can feel like running in place: most of your money is servicing interest, not paying down what you actually spent.
How to use this number
Once you see how much interest you're really paying, three moves usually make the biggest difference: increasing your monthly payment even slightly (try the Extra Payment Savings Calculator), moving the balance to a 0% or low-APR offer (see the Balance Transfer Calculator), or tackling multiple cards in the smartest order if you're carrying more than one balance (see the Snowball vs. Avalanche Calculator).
Frequently Asked Questions
How is credit card interest calculated?
Most issuers charge interest using a daily periodic rate: your APR divided by 365. Each day, that rate is applied to your outstanding balance, and the daily interest charges are added together at the end of the billing cycle. This calculator simplifies that into a monthly estimate using your current balance, APR, and payment.
Why does my balance barely go down even though I'm paying every month?
When your payment is close to the minimum, most of it is consumed by interest, leaving only a small amount to reduce the principal. As the balance slowly drops, more of each payment starts going toward principal — but on a high-APR card this can take a very long time, which is exactly what this calculator shows you.
Is this calculator accurate for my exact statement?
It provides a close estimate based on average daily balance mechanics. Your issuer may compound slightly differently (daily vs. monthly compounding, grace periods, fees), so treat the result as directionally accurate rather than penny-exact — always confirm against your official statement.
What's a good APR for a credit card?
As of 2026, the average credit card APR sits in the low-to-mid 20% range. Anything below that average is relatively good; cards in the high 20s or above cost significantly more to carry a balance on, which is why paying in full each month (or transferring the balance) matters so much.
This calculator provides estimates for educational purposes only and is not financial, tax, or legal advice. Your card issuer's actual calculation may differ slightly based on its compounding method, fees, and grace period rules — always confirm against your official statement.