Credit Card Interest Calculator

Credit card interest per day, per month and per billing cycle

Three numbers describe the same cost, and the calculator above shows all of them. The per-day figure is your balance times the daily periodic rate (APR ÷ 365). The per-month figure is the quick estimate, balance times APR ÷ 12. The per-cycle figure is the daily interest added up over the real number of days in your statement period, and it is the one that looks like your bill.

They differ because months have different lengths. Here is the same $5,000 balance at 24.99% APR under each method:

A 28-day cycle costs about $10 less than a 31-day cycle on the same balance. That gap is why your interest charge changes from statement to statement even when you have not touched the card. The APR ÷ 12 figure sits in the middle, which makes it a good planning number and a slightly rough bill predictor.

How do you convert an APR to a monthly rate?

Divide by 12. A 24.99% APR is 2.0825% a month. To get the daily rate instead, divide by 365: 24.99% ÷ 365 = 0.0685% a day. Check the daily rate against your statement, which prints it as the "daily periodic rate."

Average daily balance: a worked example

Issuers do not charge interest on the balance you had on the statement date. They charge it on the balance you carried each day, averaged over the cycle. Pay mid-cycle and the average drops. Take $5,000 at 24.99% APR over a 30-day cycle, with a $1,000 payment that posts on day 16 (the day the issuer records it, which can be a day or two after you press pay):

Interest is then $4,500 × (24.99% ÷ 365) × 30 = $92.43. With no payment it would have been $102.70, so the payment saves $10.27 this cycle, and it keeps saving every cycle that follows because the balance stays lower. Type those numbers into the calculator above to see the same figures.

The earlier the payment posts, the more days it works for you. The same $1,000 on day 1 gives an average daily balance of $4,000. On day 30 it barely moves the average. If your cash flow allows, a payment right after the statement closes beats one just before the due date, and two smaller payments can beat one large one.

Is credit card interest compounded daily?

On most cards, yes. Instead of leaving each day's interest to one side until the statement, the issuer adds it to the balance, so tomorrow's interest is charged on a slightly bigger number. Over a year, the effect on a 24.99% APR is to turn the stated rate into an effective rate of about 28.4%: (1 + 0.2499 ÷ 365)^365 − 1. Over a single 30-day cycle on $5,000 the difference is small, about $1 ($103.72 against $102.70), which is why the calculator above leaves compounding out and shows interest on today's balance.

Your cardholder agreement has the details. Look for the phrases "daily periodic rate" and "average daily balance," which tell you how your issuer figures the balance that interest applies to. The calculator is an estimate for the common method, not a copy of your issuer's system.

How to Calculate Credit Card Interest by Hand: Worked Example

Card issuers charge interest daily, and you can reproduce the math on a receipt. Take a $5,000 balance at a 24.99% APR.

Step 1: find the daily periodic rate (DPR). Divide the APR by 365: 0.2499 ÷ 365 = 0.00068466, about 0.068% per day.

Step 2: compute one day's interest. $5,000 × 0.00068466 = $3.42 per day. That is what the balance costs you every single day it remains unpaid, including weekends.

Step 3: convert to a monthly figure. The calculator above (and this page's Quick Answer) both use the simpler APR ÷ 12 method for a monthly figure: $5,000 × (24.99% ÷ 12) = $104.13, the same figure the "Monthly Interest" result above shows for these inputs. Real billing cycles run 28–31 days, so if you compute it from the daily rate times your card's actual cycle length instead, your real charge will land a few dollars either side of this depending on the exact cycle length. In practice issuers use your average daily balance, so mid-cycle payments shrink the base the daily rate applies to, which is why paying two weeks early genuinely costs less than paying on the due date.

Why did interest appear even though you paid the statement balance?

This is trailing or "residual" interest. If you carried a balance last cycle, interest kept accruing daily between the statement date and the day your payment arrived. The cure is to pay the current payoff amount (available from the issuer), not the statement balance, and then keep the card paid in full so the grace period is restored.

How Do You Stop a Balance From Growing? Three Levers to Pull

Pay more than the interest each cycle, pay earlier in the cycle, or move the balance to a lower rate. Each lever is covered below.

Does paying twice a month actually reduce interest?

Yes, mechanically. Because interest is computed on the average daily balance, a $250 payment on day 1 and $250 on day 15 produces a lower average balance than a single $500 payment on day 28: same cash, less interest. On the $5,000 example above, splitting payments typically saves a few dollars per cycle; small, but it compounds in your favor month after month.

Is a 0% balance transfer worth the fee?

Run the comparison with real numbers. Staying at 24.99% on $5,000 costs about $104 per month in interest. A transfer with a 3% fee costs $150 once. At roughly $3.42 a day, the fee pays for itself in under seven weeks, and every month of the promotional period after that is pure principal reduction, provided you make the payments that clear the balance before the promo rate expires.

Can you just ask for a lower APR?

Issuers grant rate reductions more often than most cardholders expect, particularly for accounts with on-time payment history. Even a cut from 24.99% to 19.99% reduces the daily cost on $5,000 from $3.42 to $2.74, roughly $250 saved per year for a five-minute phone call. None of these levers matter without extra cash to put toward the balance in the first place; the Budget Calculator can help find that room before you pick a strategy.