Credit Card Interest Calculator

Quick Answer

Last updated: 10 November 2026 ·How we calculate this: the daily periodic rate method

How This Credit Card Interest Calculator Works

Enter your balance, the card's APR, the length of your billing cycle and whether your card uses a 365 or 360-day year. The calculator turns the APR into a daily periodic rate and adds interest to the balance each day, the way the CFPB describes most cards working. Add a monthly payment to see how many months it takes to clear the card and how much interest you pay in total.

How to Use the Credit Card Interest Calculator

1. Enter your card balance and APR.
2. Enter the days in your billing cycle and the year basis from your card agreement.
3. Enter a monthly payment if you want a payoff plan.
4. Press Calculate.
5. Read the daily rate, this cycle's interest and the payoff time.

Credit Card Interest Formulas

• Daily periodic rate: DPR = APR ÷ 365 (or 360)
• Interest for one cycle (daily compounding): Balance × ((1 + DPR)^days − 1)
• Simple estimate: Average daily balance × DPR × days in the cycle
• Payoff: each month, new balance = balance + interest − payment

The two cycle formulas give nearly the same answer; daily compounding is slightly higher because each day's interest also earns interest.

Key Terms

• APR: annual percentage rate, the yearly cost of borrowing on the card.
• Daily periodic rate: the APR divided by 365 or 360, used to charge interest each day.
• Average daily balance: the average of the balance at the end of each day in the billing cycle.
• Grace period: the time between the end of a cycle and the due date when new purchases cost no interest if paid in full.
• Billing cycle: the period covered by one statement, usually 28 to 31 days.

Worked Example

A card has a $2,500 balance at 18% APR. The issuer uses a 360-day year, and the billing cycle is 31 days.

• Daily periodic rate = 18% ÷ 360 = 0.05000%
• Simple estimate = 2,500 × 0.00050 × 31 = $38.75
• With daily compounding, interest for the cycle = $39.04
• Paying $100 each cycle clears the card in 32 cycles, with $694.30 in interest.

Real-Life Examples

• Checking a statement: $5,000 at 22.99% builds about $95.35 of interest in 30 days.
• Planning payoff: $200 a month clears that $5,000 in 35 months, with $1,857.70 of interest.
• Bigger balances: $10,000 at 24% with $300 a month takes 56 months and costs $6,585.78 in interest.
• Comparing offers: try a balance transfer APR against your current APR to see the monthly saving.

Credit Card Interest vs Personal Loan Interest

• Credit card: interest builds daily on a revolving balance, the APR is usually higher, and there is no fixed end date.
• Personal loan: a fixed rate and fixed payments end the debt on a set date, often at a lower APR.
• Moving card debt to a loan can save interest, but only if you do not run the card balance up again.

Monthly Interest on Common Balances (30-Day Cycle, 365-Day Year)

What Changes How Much Interest You Pay

• Carrying a balance: once you carry a balance, you usually lose the grace period on new purchases too.
• APR: purchase, balance transfer, cash advance and penalty APRs can all differ on one card.
• Payment size: paying only a little more than the interest makes payoff take years.
• When you pay: paying earlier in the cycle lowers the average daily balance.
• New purchases: spending on the card while paying it down raises the interest each month.

How to Pay Less Credit Card Interest

The surest way is to pay the full statement balance by the due date every month, so the grace period applies and new purchases cost nothing. If you already carry a balance, pay as much above the minimum as you can and stop adding new spending until it is cleared.

With several cards, the avalanche method (highest APR first) saves the most interest, while the snowball method (smallest balance first) gives quicker wins. A 0% balance transfer or a lower-rate personal loan can help, but check transfer fees and what the rate becomes after the offer ends.

Common Mistakes to Avoid

• Dividing the APR by 12 only. Most cards charge interest daily on each day's balance.
• Paying only the minimum. Much of the payment goes to interest, so payoff can take years.
• Assuming a grace period while carrying a balance. It usually applies only when you paid in full last month.
• Forgetting different APRs. Cash advances and balance transfers can have their own rates.
• Adding new purchases. New spending keeps the balance and interest high.

Frequently Asked Questions

References & Sources