About Credit Interest Calculator
Credit Interest Calculator is a free tool for one straightforward job: helping you see what a credit card balance actually costs in interest. No account, no email, no sales pitch. You enter a balance and an APR, and the calculator shows the interest per day, per billing cycle, and per year.
Why this site exists
Credit card interest is quietly one of the most expensive costs many households carry, and the math behind it is not obvious from a statement. Most people never see how a single annual percentage rate turns into the finance charge that shows up each month. This site exists to make that visible, in plain language, with the formula shown openly so you can trust the number.
How the tool works
The calculator follows the standard method U.S. issuers use:
- It converts your APR into a daily periodic rate by dividing by 365 (or 360, if you choose that in the advanced options, since some card agreements use it).
- It multiplies that daily rate by your balance to get one day of interest.
- It multiplies by the number of days in your billing cycle to get the interest for the cycle, then shows daily and yearly figures alongside it.
One honest limitation: real issuers usually apply the rate to your average daily balance, which accounts for purchases and payments made during the cycle and compounds daily. This tool uses a simplified constant-balance estimate, so the result is close but will not match your statement to the penny. We show the daily periodic rate we used on every result so the math is never hidden.
How we keep it accurate
The calculation method here was checked against the U.S. Consumer Financial Protection Bureau, major issuers including Citi, and Experian's explanation of the average daily balance method. Where we reference a figure like the average credit card APR, we date it and link the source, because those numbers change. If you spot something wrong, the contact page is the fastest way to reach us. By using our tools, you agree to our Terms of Use and Privacy Policy.
How this site is built
Ready Utilities uses AI assistance for research and first drafts, then reviews, fact-checks, and directs every page before it goes live. Sources are cited directly (the CFPB, IRS, Federal Reserve, Congress.gov, and similar), every calculator's math is checked independently before it ships, and time-sensitive figures are logged with a date so they can be rechecked as they age. The tools and guides are free to use either way, this is just an honest account of how they get made.
About the author
Credit Interest Calculator is part of Ready Utilities, founded by Cedrick Reese, a retired veteran and web developer who enjoys building free, user-friendly online tools that simplify everyday tasks. His journey began in the early 2000s with affiliate marketing and niche site development, which grew into a passion for creating practical digital utilities and calculators.
After retiring, he earned a Computer Systems Technician certificate from UEI College, completed Electro-Mechanical Technologies at Tulsa Welding School, and finished the Carpentry program at Florida State College at Jacksonville. Today he combines his technical background and craftsmanship by building furniture using traditional woodworking methods, gardening, and developing helpful online tools for users worldwide.