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Interest Accrual Calculator

Calculate simple interest accrued between two dates.

Interest accrued

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What this calculator does

This calculator estimates simple interest accrued on a principal balance over a specific date range, using the actual number of days elapsed and a 365-day year convention. It's useful for estimating interest on loans, savings, bonds, or overdue balances between two known dates.

Worked example

A principal of $10,000 at 5% annual interest accrued fromJanuary 1, 2026 to July 1, 2026 (181 days) earns approximately$247.95 in simple interest.

Common mistakes

  • Mixing up day-count conventions. Actual/365, Actual/360, and 30/360 all give slightly different results — always check which one your lender or account actually uses.
  • Applying simple interest to a compounding account. Savings accounts and credit cards typically compound interest, which accrues faster than this simple-interest estimate over long periods.
  • Ignoring rate changes mid-period. A variable rate that changed partway through the date range needs to be split into separate calculations for each rate period.

Frequently asked questions

What day-count convention does this use?+

This calculator uses actual days elapsed divided by a 365-day year (the "Actual/365" convention), a common simple-interest method. Some loans and bonds use Actual/360 or 30/360 instead, which can produce slightly different results — check your loan or account terms for the exact convention used.

Is this simple interest or compound interest?+

Simple interest — interest is calculated once on the principal for the full period, without compounding. Compound interest (interest earning interest) will accrue faster over long periods, especially with frequent compounding.

What can I use this for?+

Estimating accrued interest on a loan, savings account, bond, or late payment for a specific date range — for example, "how much interest has accrued on this balance since my last statement?"

Does this account for changes in the interest rate over time?+

No — it assumes a single fixed annual rate for the entire period. For variable-rate accounts, calculate each rate period separately and add the results together.

How do you calculate accrued interest between two dates?+

Multiply the principal by the annual interest rate, then multiply by the number of days elapsed divided by 365 (principal × rate × days ÷ 365). This calculator does that automatically the moment you enter your dates and amounts.

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