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Interest Days Count Calculator

Work out interest days count instantly with clear inputs, formula shown and shareable results.

About Interest Days Count Calculator

Interest accrues per day, so the day count and the divisor both matter. From 15 January to 15 July 2026 is 181 days, and 100,000 at 6.5% yields 3223.29 on actual/365 but 3267.06 on actual/360 - the money-market basis inflating interest by about 1.4% simply through the smaller divisor.

Formulas

Simple interest

interest = principal x rate x days / divisor

Divisor

365 for sterling and most retail lending, 360 for money markets

Worked example

With the default values below, Interest Days Count Calculator returns Days Of Interest Accrual of 181. Change any input above and every figure here is recalculated in your browser.

Inputs used

Interest start date
2026-01-15
Interest end date
2026-07-15
Principalminimum 0
100,000
Annual interest rateminimum 0 %
6.5 %

Results

Days Of Interest Accrual
181 days
Interest On An Actual/365 Basis
$3,223.29
Interest On An Actual/360 Basis
$3,268.06
Daily Interest Amount
$17.8082

Step by step

  1. 1Values used
  2. 2Simple interest
  3. 3Divisor
  4. 4Days Of Interest Accrual= 181 days
  5. 5Interest On An Actual/365 Basis= 3,223.29
  6. 6Interest On An Actual/360 Basis= 3,268.06
  7. 7Daily Interest Amount= 17.8082

Assumptions and limits

  • The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
  • In particular, this calculator does not take inflation, tax or fees or charges into account.
  • Figures are rounded for display to 4 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

Why does actual/360 pay more interest?

Because dividing by 360 while counting 365 actual days overstates the year fraction by 1.39%, which favours the lender.

Which basis applies to my loan?

It is set in the agreement. Sterling and most retail lending use actual/365; USD money markets and many corporate facilities use actual/360.

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