Accrued Interest Calculator in Excel

An accrued interest Excel calculator estimates interest earned or owed between two dates using principal, an annual rate, and a day-count convention. Enter those values to calculate the accrued amount; the result is an estimate, since contracts and financial products can define day counts and accrual rules differently.

Formula

This calculator uses simple interest for a specified number of accrued days:

Accrued interest = principal × annual rate × days accrued ÷ days in year

• Principal (p): the amount on which interest accrues, in dollars.
• Annual interest rate (apr): the yearly rate entered as a percentage, such as 5 for 5%.
• Days accrued (days): the number of days in the accrual period.
• Days in year (basis): the denominator used by the selected convention, such as 365 or 360.
• Accrued interest (interest): the calculated interest, in dollars.

The rate is divided by 100 to convert a percentage into a decimal. The second output adds the unrounded calculated interest to the principal; outputs are displayed to two decimal places. This is a simple-interest estimate, not a payment schedule or an account balance that includes compounding.

Worked Example

Using the calculator’s default values—$10,000 principal, 5% annual interest, 90 days, and a 365-day year:

1. Convert the rate: 5 ÷ 100 = 0.05.
2. Multiply principal by the annual rate: $10,000 × 0.05 = $500 per year.
3. Apply the time fraction: $500 × 90 ÷ 365 = $123.2877…
4. Round the accrued interest to cents: $123.29.
5. Add it to principal: $10,000 + $123.2877… = $10,123.2877…, displayed as $10,123.29.

The calculation treats the stated rate as an annual simple rate and assumes interest accrues evenly over the entered day count.

Build the Same Calculation in Excel

Put the principal in B2, the annual rate as a percentage in B3, the accrued days in B4, and the year basis in B5. For example, enter 10000, 5%, 90, and 365 in those cells. The accrued-interest formula is:

=B2*B3*B4/B5

Format the result as currency. To show a rounded amount, use =ROUND(B2*B3*B4/B5,2). Keep the rate cell as a true percentage value; entering 5% stores 0.05, whereas entering 5 as a plain number would multiply the result by 100 unless the formula divides by 100.

If you have actual start and end dates in B4 and B5 instead, a basic elapsed-days calculation can use =B5-B4, then use that result in the interest formula. Confirm whether the applicable agreement counts the start date, end date, or both; subtracting dates alone does not establish the contractual day-count rule.

Day-Count Conventions and Excel Dates

The year basis is not universal. A 365-day basis divides by 365, while a 360-day basis divides by 360. Some calculations use the actual number of days in a period and a year basis that can vary, including 366 in a leap year. The correct convention depends on the product or agreement; do not choose one merely because it produces a preferred result.

For example, with the same $10,000 principal, 5% rate, and 90 days, the 360-day basis gives $125.00, while the 365-day basis gives about $123.29. That difference reflects the denominator, not a change in principal or annual rate. Bond calculations and other financial arrangements may also use more detailed conventions, so this simple calculator may not reproduce their settlement figures.

When This Estimate Is Useful—and Its Limits

Accrued interest is interest accumulated over time that has not yet been paid or settled. A borrower may want to estimate interest between payment dates, while an investor may want to estimate interest earned since a prior payment. In either case, the relevant principal, rate, dates, and convention must match the arrangement being estimated.

This calculator uses simple interest and a single annual rate over the full period. It does not model changing balances, variable rates, periodic compounding, partial payments, fees, grace periods, payment schedules, or adjustments specified by a contract. If interest compounds, interest may itself become part of the balance used for later calculations; use a compounding formula rather than treating the full interval as simple interest.

• Use the rate for the relevant balance and period, not a monthly rate where an annual rate is requested.
• Enter 5% as 5% in Excel, or use 5 in this calculator’s percentage input.
• Check whether the period is measured in calendar days and whether its endpoints are included.
• Use the day-count basis required by the applicable statement or agreement.
• Round for display, but avoid rounding intermediate values if matching a precise calculation.

Frequently Asked Questions

How do I calculate accrued interest in Excel?
Multiply principal by the annual rate and the number of accrued days, then divide by the applicable days-in-year basis. If the annual rate is stored as 5%, use =principal*rate*days/basis.

Should I use 360 or 365 days?
Use the convention specified for the calculation or product. A 360-day basis and a 365-day basis produce different results for the same principal, rate, and period.

Does accrued interest include compounding?
Not in this calculator. It estimates simple interest over one period. A compounding arrangement requires a formula that accounts for how often interest is added to the balance.

How can I calculate the number of accrued days from dates?
Excel can subtract an earlier date from a later date, such as =end_date-start_date. Check the applicable rules for which dates count before using the difference.

Why does my Excel answer differ from a statement?
Possible reasons include a different day-count convention, date inclusion, compounding, rate, balance, or rounding method. Compare the inputs and calculation rules with the statement or agreement rather than assuming the spreadsheet is using the same method.

Assumptions

• The annual rate is fixed throughout the entered period.
• Interest accrues evenly using simple interest; no payment timing or periodic compounding is modelled.
• The selected year basis is the denominator for the entire period.
• Fees, taxes, changing balances, and contract-specific adjustments are not included.

This result is an estimate; the relevant statement or agreement gives the applicable calculation and exact figures.

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in p | Principal | $ | 10000 | 0 | 100000000
in apr | Annual interest rate | % | 5 | 0.01 | 100
in days | Days accrued | days | 90 | 0 | 36500
in basis | Days in year | days | 365 | 360 | 366
out interest | Accrued interest | $ | p * (apr / 100) * days / basis | 2
out total | Principal plus accrued interest | $ | p + interest | 2