Accrued Interest Calculator
Estimate interest accrued between two dates for savings, loans, notes, or bond-style calculations.
What Is Accrued Interest?
Accrued interest is interest that has been earned or charged over time but has not yet been paid. If you hold an interest-bearing asset, accrued interest is what you have earned since the last payment date. If you owe money, accrued interest is the amount added to your balance for the same period.
In plain English: interest builds up every day (or every period), even if money changes hands only once a month, quarter, or year.
How This Calculator Works
This accrued interest calculator uses four essential inputs:
- Principal: The base amount earning or accruing interest.
- Annual rate: The yearly interest rate as a percentage.
- Date range: The period over which interest is accrued.
- Day count convention: The rule for converting calendar days to a fraction of a year.
You can also choose simple interest or periodic compounding. For many short date ranges, the difference is small; for longer periods, compounding can increase accrued interest significantly.
Core Formula (Simple Interest)
For simple accrued interest, the calculator applies:
Accrued Interest = Principal × (Rate ÷ 100) × (Days ÷ Year Basis)
Compounded Formula
If compounding is selected, it uses:
Future Value = Principal × (1 + (Rate ÷ 100) ÷ n)^(n × t)
Accrued Interest = Future Value − Principal
where n is compounding periods per year and t is the fraction of a year from the chosen day count basis.
Why Day Count Conventions Matter
Day count conventions are widely used in lending and bond markets. They define two things:
- How to count the number of days in the period.
- What number to use for “days in a year” (typically 360 or 365).
A change in convention can alter accrued interest enough to matter in professional finance.
Common Conventions
- Actual/365: Uses actual calendar days over a 365-day year basis.
- Actual/360: Uses actual days but divides by 360; often yields slightly higher interest than Actual/365 for the same dates.
- 30/360: Assumes each month has 30 days and each year has 360 days; common in fixed income calculations.
Example: Quick Scenario
Suppose you have $25,000 at 6.25% annual interest from January 1 to April 1. Using simple interest and Actual/365, interest accrues daily across the date span and is then scaled by 365. If the same scenario used Actual/360, the denominator is smaller, and interest comes out a bit higher.
That difference is exactly why analysts, accountants, and lenders explicitly state day count methods.
When to Use an Accrued Interest Calculator
- Estimating interest owed between loan payment dates.
- Calculating bond transaction settlement amounts.
- Forecasting savings growth over partial periods.
- Reconciling statements when payment cycles are irregular.
- Auditing amortization or interest schedules.
Common Mistakes to Avoid
1) Mixing monthly rates with annual formulas
Enter an annual percentage rate in this calculator. If your rate is monthly, convert it first.
2) Ignoring date order
End date must be after start date. Reversed dates will produce invalid results.
3) Using the wrong day count basis
Contracts, bonds, and banks may each use different conventions. Use the one specified in your agreement.
4) Confusing accrued with paid
Accrued interest is earned/owed to date; it may not yet be paid or posted.
Final Thoughts
Understanding accrued interest gives you a clearer picture of real financial performance. Whether you are managing debt, pricing a bond trade, or tracking investment earnings, accurate period-by-period calculations can improve planning and decision-making.
Use the calculator above for fast estimates, then validate with your institution’s method when exact contractual precision is required.