About the Interest Between Two Dates Calculator
This calculator works out the interest that accrues on a sum of money between two specific dates. Enter the principal, the annual interest rate, the start and end dates and how interest is counted, and it returns the interest, the closing balance, the exact number of days and the year fraction used. It handles both simple interest (charged only on the original principal) and compound interest with daily, monthly, quarterly or annual compounding.
Use it to check interest on a savings deposit or CD that was open for part of a year, to price a short-term personal loan between friends, to work out interest owed on an overdue invoice, or to see how a bank arrived at a figure on your statement. Because banks and lenders count days differently, you can choose the day-count convention: Actual/365 is standard for UK and many consumer accounts, Actual/360 is common for US commercial loans and money markets, Actual/Actual splits the period by calendar year, and 30/360 is used for many bonds and mortgages.
The start date is excluded and the end date is included, which is how interest is normally accrued (a deposit made on 1 March and withdrawn on 2 March earns one day of interest). The rate is assumed fixed for the whole period.
With the default inputs, the interest is $247.95. Change any value above to recalculate instantly.
How to use the interest between two dates calculator
- 1Enter the principal and the annual interest rate.
- 2Pick the start and end dates of the period.
- 3Choose simple or compound interest (and the compounding frequency).
- 4Select the day-count convention your bank, lender or contract uses.
- 5Read the interest, the number of days and the year fraction used.
Formula and method
The year fraction t converts the period between the two dates into years. Actual/365 divides the actual number of days by 365; Actual/360 divides by 360 (so a full year counts as 365/360 of a year and accrues slightly more); Actual/Actual (ISDA) splits the period at each 1 January and divides the days in each calendar year by 365 or 366; and 30/360 treats every month as 30 days and the year as 360 days.
Simple interest multiplies principal, annual rate and year fraction. Compound interest grows the principal by (1 + r/k) for each of the k × t compounding periods in the span, where k is 12 for monthly, 4 for quarterly, 1 for annual, and 365 (or 360 on a 360-day basis) for daily compounding. Partial periods are handled with fractional exponents. The start date is excluded and the end date included.
- I
- Interest accrued
- P
- Principal
- r
- Annual interest rate (decimal)
- t
- Year fraction from the day-count convention
- k
- Compounding periods per year
Worked examples
$10,000 at 5% simple, 15 Jan to 15 Jul 2026
There are 181 days between 15 January and 15 July 2026. Simple interest is 10,000 × 0.05 × 181/365 = $247.95.
$25,000 at 4.5% compounded daily for one year
Daily compounding over 365 days gives 25,000 × ((1 + 0.045/365)^365 − 1) = $1,150.62, about $25 more than simple interest of $1,125.
Actual/360 loan: $100,000 at 6%, 1 Feb to 1 May 2026
The period is 89 actual days. On an Actual/360 basis the interest is 100,000 × 0.06 × 89/360 = $1,483.33.
30/360 bond basis: $50,000 at 7%, 31 Oct 2027 to 31 Mar 2028
Under 30/360 both month-end dates become the 30th, so the period counts as exactly 5 months of 30 days = 150/360 of a year. Interest is 50,000 × 0.07 × 150/360 = $1,458.33, even though 152 calendar days pass.
Actual/Actual across a leap year, compounded monthly
The 61 days in 2027 count as 61/365 and the 121 days in leap year 2028 as 121/366, a year fraction of 0.4977. Monthly compounding at 5% gives $502.91.
Frequently asked questions
How do I calculate interest between two dates?+
Count the days between the dates (excluding the start date, including the end date), divide by the year basis to get a year fraction, then multiply principal × annual rate × year fraction for simple interest. For compound interest use P × ((1 + r/k)^(k × t) − 1).
What is the difference between Actual/365 and Actual/360?+
Both use the real number of days, but Actual/360 divides by 360 instead of 365. That makes each day worth 1/360 of the annual rate, so a full year accrues about 1.4% more interest. US commercial loans and money market instruments often use Actual/360.
Is the start date or end date counted?+
Normally interest accrues for each night the money is held, so the first day is excluded and the last day included. From 1 March to 31 March is 30 days of interest. Some loan agreements count both days; add one day to the end date to model that.
What day count do savings accounts use?+
Most UK, Canadian, Indian and US consumer savings accounts calculate interest daily on an Actual/365 basis (some use 366 in leap years) and pay it monthly or annually. The account terms or your bank’s interest disclosure confirm the method.
How do I calculate daily interest?+
Daily interest = principal × annual rate ÷ 365 (or 360). On $10,000 at 5% that is $1.37 per day on an Actual/365 basis, or $1.39 on Actual/360.
Results are estimates for educational purposes and are not financial advice. Rates, fees and terms vary — confirm with your lender or a licensed advisor before making decisions.