Credit Card Interest Calculator
Estimate how much of your next payment goes to interest versus principal — and what your balance could cost you over time.
Updated · Published · Built by Ali Ahmad, Founder
Calculation method: This calculator uses a simplified monthly-interest model (APR ÷ 12). Credit-card issuers may calculate interest using daily periodic rates and average daily balances, so your actual statement may differ. See our methodology.
Credit Card Interest Calculator
A credit card interest calculator estimates how much of each payment goes to interest versus principal, your total interest cost, and how long payoff will take. To calculate credit card interest for one month, multiply your balance by your APR and divide by 12: $5,000 at 24.99% APR is about $104 of interest this month. The calculator repeats that every month using your balance, APR, and a fixed monthly payment.
If you carry a balance, most people only see the final interest figure on their statement, without understanding why so little of each payment seems to move the balance. This calculator estimates that breakdown so you can see where your money is going.
How the Calculator Works
You enter three numbers: your current balance, your card's APR (annual percentage rate), and the fixed monthly payment you plan to make. The calculator then:
- Converts your APR into a monthly rate by dividing it by 12.
- Multiplies that rate by the balance at the start of the month to estimate that month's interest.
- Subtracts the interest from your payment; whatever is left reduces the principal.
- Repeats month by month until the balance reaches zero (or flags it if your payment doesn't cover the interest).
The results show how much of your next payment is interest, your total interest if you keep paying the same amount, and the number of months to a zero balance.
How to Calculate Credit Card Interest (Formula)
Principal Paid = Payment − Monthly Interest
New Balance = Balance − Principal Paid
This is a simplified estimate, not an issuer-specific statement calculation. Many issuers instead apply a daily periodic rate (APR ÷ 365) to your average daily balance. Not sure whether to enter your APR or your interest rate? See APR vs. interest rate.
Example: $5,000 at 24.99% APR, paying $150 a month
The monthly rate is 24.99% ÷ 12 ≈ 2.08%. In month one, interest is $5,000 × 0.020825 = $104.125, so only $45.875 of the $150 payment reduces the balance. The calculator above and the table round the interest to the cent first ($104.13) and show the rest of the payment as principal ($45.87), so the two always add up to exactly $150. As the balance shrinks, the interest share falls and the principal share grows.
| Month | Payment | Interest | Principal | Balance |
|---|---|---|---|---|
| 1 | $150.00 | $104.13 | $45.87 | $4,954.13 |
| 2 | $150.00 | $103.17 | $46.83 | $4,907.29 |
| 3 | $150.00 | $102.19 | $47.81 | $4,859.49 |
| 12 | $150.00 | $92.45 | $57.55 | $4,381.86 |
| 24 | $150.00 | $76.30 | $73.70 | $3,590.26 |
| 36 | $150.00 | $55.62 | $94.38 | $2,576.54 |
| 48 | $150.00 | $29.14 | $120.86 | $1,278.36 |
| 58 (final) | $72.30 | $1.47 | $70.82 | $0.00 |
At this payment, the balance reaches zero in about 58 months (4 years, 10 months), with roughly $3,622 in total interest on top of the original $5,000.
When the Result May Differ
Treat the results as a planning estimate. Your real numbers can differ because of:
- Daily periodic rate: many issuers apply APR ÷ 365 (or 360) each day instead of APR ÷ 12 once a month, which can produce different interest.
- Average daily balance: your balance moves during the cycle as purchases post and payments arrive; this calculator uses a single month-start balance.
- Fees: annual, late, foreign-transaction, cash-advance, and balance-transfer fees aren't included unless the calculator asks for them.
- New purchases: the estimate assumes you stop adding charges. Any new spending lengthens payoff and raises interest.
- Grace period: whether new purchases accrue interest depends on whether you pay your statement balance in full and on your card's terms.
- Different APR categories: purchases, balance transfers, cash advances, and penalty APRs can carry different rates on the same card, and how payments are allocated between them affects the total.
Your statement and cardholder agreement are the final word. See our methodology for how every calculator on this site works.
Daily or Monthly: How Do Card Issuers Charge Interest?
Many issuers charge interest daily: they divide your APR by 365 (or 360) and apply that daily rate to your balance each day of the billing cycle, usually using the average daily balance. Because each day's interest is added to the balance, it compounds daily. The monthly method used here (APR ÷ 12) gives a very close planning estimate; to see the daily figure, use the Daily Periodic Rate Calculator. For a step-by-step worked example of both methods, read how to calculate credit card interest by hand, or download our free Excel template.
How to Lower Your Interest Cost
Three moves usually make the biggest difference: raising 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 paying multiple cards in the most efficient order (see the Snowball vs. Avalanche Calculator). For the daily-rate view, use the Daily Periodic Rate Calculator. To stop paying interest on new purchases altogether, see how to avoid credit card interest.
Frequently Asked Questions
How is credit card interest calculated?
Many issuers use a daily periodic rate: your APR divided by 365 (sometimes 360), applied to your average daily balance for each day of the billing cycle. This calculator simplifies that to a monthly rate (APR ÷ 12) applied to your balance, which works well for planning but may not match your statement to the cent.
Why does my balance barely go down even though I'm paying every month?
When your payment is close to the interest charge, most of it covers interest and only a small amount reduces the principal. On a $5,000 balance at 24.99% APR, about $104 of a $150 payment goes to interest in the first month. As the balance falls, more of each payment goes to principal.
Is this calculator accurate for my exact statement?
No — it provides an estimate using a simplified monthly-interest model (APR ÷ 12). Many issuers calculate interest with a daily periodic rate applied to your average daily balance, and grace periods and fees also vary, so treat the result as a planning estimate rather than a statement-exact figure — always confirm against your official statement.
Does this calculator include new purchases or fees?
No. It assumes you make no new charges and pay no fees while paying down the balance. New purchases, annual fees, or late fees would raise the balance and the interest, and lengthen payoff.
How do I avoid paying credit card interest?
On cards with a grace period, paying your full statement balance by the due date each month typically avoids interest on purchases. If you already carry a balance, paying more each month, or moving it to a lower-rate offer, reduces the interest you pay.
What's a good APR for a credit card?
It depends on your credit profile and the type of card. For context, the Federal Reserve's G.19 data put the average rate at 21.19% across all accounts and 22.36% on accounts charged interest in Q3 2026. The higher your APR, the more it matters to pay in full or pay the balance down quickly.
What if my payment doesn't cover the interest?
If your monthly payment is smaller than the monthly interest, the balance never goes down. The calculator flags this so you know the payment needs to increase.
This calculator provides estimates for educational purposes only and is not financial, tax, or legal advice. Most results use a simplified monthly-interest model (APR ÷ 12); your card issuer may use a daily periodic rate and average daily balance, plus its own fees and grace period rules, so your actual figures may differ — always confirm against your official statement.
Sources
- What is a grace period for a credit card? — Consumer Financial Protection Bureau. Checked September 25, 2026.
- Regulation Z § 1026.53 – payments above the minimum go to the highest-APR balance first — Consumer Financial Protection Bureau. Checked September 25, 2026.
- Consumer Credit – G.19 (credit card interest rates, Q3 2026) — Federal Reserve Board. Checked October 25, 2026.