Daily Compound Interest Calculator
Day-by-day compounding in any currency, with a full schedule.
🔒 100% browser-based — your data never leaves your device.
About this tool
Enter a starting amount, a compounding rate per day and how many days to run, and this calculator builds the whole schedule: the balance on day 1, day 2, and every day through day N, with the interest earned each day. Pick your currency and the amounts are formatted the way that currency is normally written, so a Korean won figure shows no decimals while a US dollar figure shows two.
The formula is the standard compound growth one: balance = principal × (1 + rate)^days, where the rate is applied once per day. A negative rate works too, which is useful for modelling steady decay rather than growth. You can download the full schedule as a CSV, and optionally convert the final balance into a second currency using live reference rates.
Frequently asked questions
What is the difference between simple and compound interest?
Simple interest always pays on the original amount. Compound interest pays on the balance including interest already earned, so each day the base is slightly larger. Over a long run the gap becomes enormous.
How do I convert an annual rate to a daily rate?
For true equivalence use rate_daily = (1 + rate_annual)^(1/365) − 1. A 10% annual return is about 0.02612% per day, not 10/365 = 0.0274%. Dividing by 365 slightly overstates the result.
Why does the table skip rows for long periods?
Beyond 200 days the table shows the first ten days, then evenly spaced checkpoints, then the final day, so the page stays readable. The CSV download always contains every single day.
Does this send my numbers anywhere?
No. The calculation runs entirely in your browser. If you choose a conversion currency, the page downloads a public exchange-rate table from open.er-api.com — that request contains no amounts, dates or any other input of yours.
Can I use this for a savings account or a loan?
It models pure compounding with no deposits, withdrawals, fees or taxes. Real products add all of those, so treat this as an educational tool rather than a projection of what you would actually receive.