Credit Card Interest Calculator

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 this calculator's own "Monthly Interest" result shows for these inputs, before you have bought anything new. 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

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.