Credit Card Interest Calculator
Created by: Emma Collins
Last updated:
Calculate how much interest your credit card balance costs per day, per month, and per year using your APR and the daily periodic rate. See the cost of carrying the balance for 3, 6, or 12 months and how your payment splits between interest and principal.
Credit Card Interest Calculator
FinanceSee what your balance costs per day, month, and year — and how much of your payment actually reduces the debt.
The purchase APR from your latest statement. The U.S. average on interest-assessed accounts is roughly 21–24%.
What you plan to pay each month — used to split interest vs principal and estimate payoff time.
What Is a Credit Card Interest Calculator?
A credit card interest calculator shows what carrying a balance actually costs.
Using your balance and APR, it computes the daily periodic rate, the interest accruing each day, month, and year, and the total cost of carrying the balance for 3, 6, or 12 months.
It also splits your monthly payment into the portion consumed by interest and the portion that actually reduces your balance — a number that surprises most cardholders.
Understanding this cost-of-carrying math is the first step toward deciding whether to pay the balance down aggressively, transfer it, or restructure the debt.
How Credit Card Interest Is Calculated
Card issuers divide your APR by 365 to get a daily periodic rate, then apply it to your average daily balance across the billing cycle.
This calculator approximates that with monthly interest = balance × APR ÷ 12 and daily interest = balance × APR ÷ 365, which closely matches issuer math when the balance is stable across the cycle.
The carry scenarios assume you pay only the interest each month, keeping the balance flat — the true cost of treating a credit card as a standing loan.
If you enter a monthly payment, the calculator also simulates the payoff month by month: interest accrues, your payment is applied, and the remainder reduces principal, producing an estimated payoff time and total interest.
Credit Card Interest Formulas
Daily periodic rate (DPR) = APR ÷ 365
Daily interest = Balance × DPR
Monthly interest ≈ Balance × APR ÷ 12
Annual interest ≈ Monthly interest × 12
Principal reduction = Payment − Monthly interest
Carry cost (interest-only) = Monthly interest × Months carried
Example Scenarios
The $5,000 Balance at 24% APR
A $5,000 balance at 24% APR accrues $3.29 per day — about $100 per month and $1,200 per year. Carrying it for 12 months while paying only the interest costs $1,200 with the debt no smaller than when you started. A $250 monthly payment puts $150 toward principal and clears the debt in about 24 months with roughly $1,300 of total interest.
Store Card at 29.99% APR
A $2,000 store-card balance at 29.99% APR accrues about $50 per month. A $60 minimum-style payment leaves only $10 for principal — 83% of the payment is interest. Doubling the payment to $120 sends $70 to principal and cuts the payoff from over a decade to about 20 months. High-APR store cards are usually the top priority in any avalanche-style payoff plan.
The Grace Period Advantage
A cardholder spends $3,000 per month but pays the statement balance in full every cycle. Annual interest paid: $0, thanks to the grace period. A neighbor with the same spending who carries an average $3,000 revolving balance at 22% APR pays about $660 per year. Same card, same spending — the difference is entirely whether the statement balance is cleared before the due date.
How People Use This Calculator
- Seeing the real daily and monthly cost of a balance before deciding how aggressively to pay it down
- Comparing the cost of carrying a balance for 3, 6, or 12 months against a 0% balance-transfer offer
- Understanding why minimum-sized payments barely move the balance
- Estimating payoff time and total interest at your current monthly payment
- Prioritizing which card to attack first in a debt-avalanche plan
Tips for Cutting Credit Card Interest
Attack the APR, not just the balance.
A balance transfer to a 0% intro-APR card (typically 12–21 months, with a 3–5% transfer fee) or a consolidation loan at 10–14% can cut the interest cost of the same debt by more than half.
Run the numbers before assuming the transfer fee is worth it — our balance transfer break-even calculator does exactly that.
Every extra dollar you pay goes entirely to principal.
Because interest is charged on the balance, a payment increase from $150 to $250 on a $5,000 balance at 24% APR does not cut payoff time by 40% — it cuts it by more than half, because the extra $100 compounds by shrinking every future month’s interest charge.
These figures are planning estimates.
Issuers differ on average-daily-balance details, fee posting, and whether they use 360 or 365 days.
Your statement’s interest-charge box is the authoritative number — this calculator explains it and projects it forward.
Frequently Asked Questions
How is credit card interest calculated?
Most issuers use the average daily balance method with a daily periodic rate. Your APR is divided by 365 to get the daily rate, which is applied to your balance each day of the billing cycle. A $5,000 balance at 24% APR accrues about $3.29 per day — roughly $100 per month. This calculator uses your balance and APR to estimate daily, monthly, and annual interest costs so you can see what carrying the balance really costs.
What is a daily periodic rate (DPR)?
The daily periodic rate is your APR divided by 365 (some issuers use 360). A 24% APR equals a DPR of about 0.0658%. Each day, the issuer multiplies your balance by the DPR and adds that interest to what you owe at the end of the cycle. Because interest accrues daily, balances compound faster than a simple monthly calculation suggests, which is why carrying a balance is so expensive.
Why does so little of my payment go to principal?
Your payment first covers the interest that accrued during the billing cycle, and only the remainder reduces your balance. On a $5,000 balance at 24% APR, roughly $100 of a $150 payment goes to interest, leaving just $50 for principal — only a third of your payment actually reduces the debt. Increasing your payment goes almost entirely to principal, which is why even modest payment increases dramatically shorten payoff time.
How can I avoid paying credit card interest entirely?
Pay your statement balance in full by the due date every month. Most cards offer a grace period on purchases — typically 21 to 25 days between the statement close and the due date — during which no interest accrues on new purchases. The grace period is generally lost once you carry a balance, meaning new purchases start accruing interest immediately until you pay in full for one or two consecutive cycles.
What is a typical credit card APR right now?
Average APRs on accounts assessed interest have run between 21% and 23% in recent years according to Federal Reserve G.19 data, with many retail store cards charging 28% to 32%. Your rate depends on your credit profile and the card type. Because card APRs are variable and tied to the prime rate, they move when the Federal Reserve changes rates — verify your current APR on your latest statement.
Does carrying a small balance help my credit score?
No — this is a persistent myth. Paying in full each month builds credit history just as effectively as carrying a balance, without costing you interest. Your utilization is reported from your statement balance, so the account shows activity even when you pay in full. Carrying a balance only means paying interest for no scoring benefit. Keeping reported utilization low and payment history spotless are what actually drive your score.
Is credit card interest tax deductible?
Personal credit card interest is not tax deductible — that deduction was eliminated by the Tax Reform Act of 1986. Interest on business purchases charged to a card can be deductible as a business expense if you are self-employed and the purchases are legitimate business costs. Keeping business and personal spending on separate cards makes that documentation dramatically easier if you are ever asked to substantiate the deduction.
Sources and References
- Consumer Financial Protection Bureau: How does my credit card issuer calculate the amount of interest I owe? — consumerfinance.gov
- Federal Reserve: Consumer Credit — G.19 Statistical Release (average credit card interest rates)
- Truth in Lending Act, Regulation Z (12 CFR Part 1026) — periodic rate and APR disclosure requirements