Credit Card Interest Calculator

How to use this calculator

Choose your mode from the tabs. Fixed Payment mode calculates payoff time and total cost when you make a consistent monthly payment. Minimum Payment mode simulates the slow, expensive payoff that results from only paying the minimum required each month.

Current Balance is what you owe today. Use the statement balance or your current outstanding balance — whichever is most accurate.

APR (%) is your card’s Annual Percentage Rate. This is typically printed on your statement. Average US credit card APR was around 21-24% in 2024. If you have multiple cards, run the calculator separately for each.

Monthly Payment (Fixed Payment mode) is the amount you commit to paying each month. For fastest results, enter the highest amount you can consistently afford. It must exceed the monthly interest charge to make any progress on the principal.

Minimum Payment % (Minimum Payment mode) is the percentage of the balance the bank uses to set your minimum. Most issuers use 1-2% of the balance plus the monthly interest. This calculator defaults to 1% with a $25 floor, matching a common industry formula.

Additional Monthly Purchases simulates ongoing spending on the card while you pay it off. Adding purchases extends payoff time significantly and is the most common reason minimum payment strategies fail to make progress.

What credit card interest is and how it compounds

Credit card interest is not straightforward. Most cards use a Daily Periodic Rate (DPR), calculated by dividing the APR by 365. Each day, your average daily balance is multiplied by the DPR to accrue interest. At the end of the billing cycle, all the daily interest charges are summed and added to your balance.

This means credit card interest effectively compounds daily. You are paying interest on interest every single day. The distinction from a monthly calculation is small — about 0.04% on a 20% APR — but it adds up over years.

If you carry a $5,000 balance at 20% APR for 12 months and make no payments, your balance grows to $6,107 with daily compounding versus $6,000 with simple interest. The $107 difference seems minor. Over 5 years with no payments, the daily compounding balance becomes $13,591 versus $10,000 with simple interest. The gap widens every year.

The statement interest charge you see each month is: Balance × (APR / 12). That approximates the daily compounding effect in a single monthly number. This calculator uses the monthly rate for simulating month-by-month payoff schedules.

The formula

Daily interest rate:

Monthly interest charge (approximation):

Principal paid per month:

Minimum payment calculation (common issuer formula):

For a fixed payment, the number of months to payoff is:

This closed-form only works when there are no new purchases. The calculator uses a month-by-month simulation to handle new purchases accurately.

Fixed payment vs minimum payment: a direct comparison

The most important calculation you can run with this tool is the minimum payment simulation. Most people systematically underestimate how expensive minimum payments are.

The minimum payment row is always dramatically worse. For a $10,000 balance at 24%, minimum payments take 271 months (22+ years) and cost $17,411 in interest — nearly twice the original balance. A fixed $300/month cuts both the time and interest cost by more than 70%.

The reason is structural. The minimum payment is tied to the balance. As the balance slowly falls, the minimum payment falls with it. You end up making smaller and smaller payments while the interest charge shrinks only slightly. Progress on the principal is almost imperceptible in the early months.

Real-world examples

The cost of carrying a balance for one year

Many people think of credit card interest as a small cost they will deal with later. Here is the annual cost at different balance levels.

The payoff acceleration from one extra payment

A common piece of advice is to pay a bit more than the minimum. Here is the concrete impact.

Comparing two payoff strategies

You have $15,000 in credit card debt across two cards:

Card A: $10,000 at 24% APR Card B: $5,000 at 19% APR

You have $500/month to put toward debt. Should you split it evenly or focus on one card?

Common mistakes

Paying only the minimum and assuming you are managing the debt. The minimum payment is designed to maximize revenue for the card issuer, not to help you pay off debt. It is the slowest and most expensive payoff path available to you. It is not a debt management strategy.

Making purchases on a card you are actively paying down. New purchases restart the interest clock on those dollars. If you are paying off a card, freeze the spending on it. Use a different card for new purchases or switch to cash/debit until the balance is zero.

Ignoring the grace period. If you pay the full statement balance by the due date, most cards charge zero interest on new purchases. This grace period disappears if you carry a balance. Once you carry any balance, interest starts accruing on new purchases immediately, before your next payment.

Missing a payment. A missed payment typically triggers a penalty APR (often 29.99%) that can persist for 12+ months. At penalty APR, even a modest balance becomes enormously expensive. Set up autopay for at least the minimum to prevent this.

Balance transfer math errors. A 0% balance transfer sounds free but usually carries a 3-5% transfer fee. On a $10,000 transfer, that is $300-500 upfront. If the 0% period is 12 months, you need to pay off at least $833/month to clear the balance before the standard APR kicks in.

When does it make sense to carry a balance?

In almost no case. The scenarios where it might be rational:

0% promotional APR period. If you have a genuine 0% period and the math works (you will pay it off before the rate resets), carrying the balance during that period while keeping cash invested is technically optimal. The risk is forgetting and getting hit with standard APR at the end.

Short-term cash flow bridge. If you have money incoming within 30 days and need to float a purchase, a single billing cycle at 20% APR on $1,000 costs about $17. That is not catastrophic. The error is when “one month” turns into twelve.

No better options. If the alternative is missing rent or a utility bill, a credit card balance at 20% is better than the late fees, disconnection fees, and credit damage of missing those payments.

Outside of these narrow cases, carrying a credit card balance is a high-cost form of borrowing. The rates are typically 15-30% — far above personal loans, HELOCs, auto loans, or mortgages. Prioritizing credit card payoff before any other financial goal (beyond an emergency fund) is almost always the mathematically correct move.

The bottom line

Credit card interest is expensive. The daily compounding, the high APRs, and the minimum payment structure all work against the cardholder. The numbers in this calculator are not abstract — they are the actual dollars that will leave your account if you do not pay off the balance.

The single most important number in the results is months to payoff. If it shows 100+ months, the payment is too low. If it shows “balance may never be paid off,” the monthly interest alone exceeds your payment. Both situations require immediate action: increase the payment, reduce new spending, or both.

The most powerful move you can make is to increase your monthly payment above the minimum as soon as possible. Even $50 or $100 extra per month can cut years off the payoff and save thousands in interest. The calculator shows exactly how much.