Work out interest days count instantly with clear inputs, formula shown and shareable results.
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.
Simple interest
interest = principal x rate x days / divisor
Divisor
365 for sterling and most retail lending, 360 for money markets
Because dividing by 360 while counting 365 actual days overstates the year fraction by 1.39%, which favours the lender.
It is set in the agreement. Sterling and most retail lending use actual/365; USD money markets and many corporate facilities use actual/360.