Enter a principal, annual rate, and number of days, plus an optional daily contribution, to find the future value and total interest.
How to Use the Daily Compound Interest Calculator
Enter the starting principal, annual interest rate, and number of days, then optionally add a daily contribution amount. Future value, total contributed, and total interest update as any field changes.
Daily compounding applies interest to the balance once per day rather than once per month or once per year, so each day's interest is calculated on a slightly larger balance than the day before — including whatever interest already accrued.
Growing the Principal
Daily Rate = Annual Rate ÷ 100 ÷ 365
Principal's Future Value = Principal × (1 + Daily Rate)^DaysA $2,000 principal at 5% annual, compounded daily for a full year, grows to a little over $2,102 — about $102.50 in interest on its own, close to but not exactly 5% of the starting balance, because interest earns interest along the way.
Adding Daily Contributions
Contribute a fixed amount every single day and those contributions compound too, just with less time to grow than the original principal:
Contributions' Future Value = Daily Contribution × (((1 + Daily Rate)^Days − 1) ÷ Daily Rate)Leave the contribution field at zero and this term drops out entirely — the calculator just shows growth on the principal alone.
Total Contributed vs. Total Interest
Total contributed is simply the principal plus every daily contribution added up, with no growth applied — a baseline to measure interest against. Total interest is whatever the future value exceeds that baseline by. Watching how that interest figure changes as the day count stretches out past a year or two is the clearest way to see daily compounding's actual effect, rather than taking a quoted "5% APY" label at face value.