Accrued interest and supporting figures
The principal stays constant throughout the accrual interval. Actual days are entered directly; selecting 360 changes the denominator without converting calendar dates to a 30/360 convention.
For interest over a longer year-based interval, use the Simple Interest Calculator with matching simple-interest assumptions.
The formula
The principal stays constant throughout the accrual interval. Actual days are entered directly; selecting 360 changes the denominator without converting calendar dates to a 30/360 convention.
Worked accrued interest example
A 10,000 balance at 5% over 30 actual days earns 41.10 on Actual/365, or 41.67 on Actual/360. Neither estimate compounds interest.
How to use this calculator
- Enter principal balance, annual interest rate, accrual days.
- Set annual day-count basis using the stated units or choices.
- Calculate and compare accrued interest, principal plus interest, interest per day.
Choosing inputs for accrued interest
Day-count basis is part of a financial agreement, rather than a choice that makes one result universally correct. Count the days for which interest applies under the contract, then choose the denominator used by that agreement. The same balance, annual rate, and calendar interval produce different interest when the denominator changes.
A constant balance works for an interest accrual between transactions. If a payment, withdrawal, or deposit changes the principal during the interval, split the interval into separate periods and add the interest for each period. Do not enter the final balance for every day when earlier balances differed.
Interpreting accrued interest
Accrued interest is the amount attributable to elapsed time, even if it has not yet been paid. Principal plus interest describes a combined amount under this simple-interest model; it does not imply that a bond trades at that amount or that a lender will capitalize the charge.
Assumptions & limitations
What this calculation assumes
- The annual percentage rate is a simple nominal rate.
- Days are whole actual accrual days and the balance remains unchanged.
What to keep in mind
- The tool does not implement 30/360 date adjustment, Actual/Actual, coupon schedules, or daily compounding.
Common questions
Is Actual/360 the same as 30/360?
No. Actual/360 uses the actual day count divided by 360; 30/360 changes how dates are counted.
Does a leap year change Actual/365?
A fixed Actual/365 basis continues to divide by 365. An Actual/Actual agreement needs another method.
Should the payment day count as an accrual day?
Follow the agreement’s date inclusion rule. Enter the resulting actual day count; this tool does not infer it from calendar dates.
Sources & further reading
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