How this number is made
If you carry a balance, a month of interest is about the balance times the APR divided by 12. Issuers often use a daily rate and an average daily balance, so the statement can differ by a few dollars.
- The balance is what you revolve, not new purchases inside a grace period you are still inside.
- APR is the purchase APR on the statement.
Formula
A month of interest ≈ balance × APR ÷ 12.
Worked example
With the figures already in the form, about one month of interest is $57.25.
Questions
What about the grace period?
If you pay the statement in full and the card grants a grace period, new purchases may accrue nothing. This page is for a balance that is revolving.
Why not the daily rate?
A daily rate of APR ÷ 365 times each day’s balance is more precise. This is the one-line version.