What This Calculator Does
The Average Daily Balance Finance Charge Calculator estimates the interest a credit card issuer bills for a single statement period. Most U.S. card issuers use the average daily balance method: they track your balance each day of the cycle, average it, then multiply by a daily periodic rate and the number of days in the cycle. This tool reproduces that math so you can verify your statement or plan a payoff.
How to Use It
Enter three values: your average daily balance (the issuer usually prints this on your statement), the card's APR as a percentage, and the number of days in the billing cycle (commonly 28–31). The calculator returns the finance charge for the cycle plus the daily periodic rate and the per-day interest amount.
The Formula Explained
The core equation is $$\text{Charge} = \text{Average Daily Balance} \times \frac{\text{APR}}{365} \times \text{Days in Cycle}$$ APR \(\div\) 365 gives the daily periodic rate (the slice of yearly interest applied each day). Multiplying by the average balance gives one day's interest, and multiplying by the number of days totals the charge for the whole cycle.
Worked Example
Suppose your average daily balance is $1,000, your APR is 19.99%, and the cycle is 30 days. The daily periodic rate is \(0.1999 \div 365 \approx 0.00054767\). One day of interest is \(\$1{,}000 \times 0.00054767 \approx \$0.5477\). Over 30 days the finance charge is about $16.43.
FAQ
Why divide by 365? Most issuers use a 365-day year for the daily periodic rate; a few use 360, which slightly increases the charge.
Where do I find my average daily balance? It is typically listed in the interest-charge section of your monthly statement.
Does paying early reduce the charge? Yes—because each day's balance counts, lowering the balance earlier in the cycle reduces the average and the resulting interest.
