I'm using this formula to determine total interest due on a bank CD:

=ISPMT(A2/365,A4-A3,1,A1)

A1 = amount of CD

A2 = interest rate

A3 = inception date

A4 = maturity date

Tried one manually, doesn't match the formula -

$10,000 @ 5% from 1/1/05 to 2/1/05

= (.05/365)(31)(10000) = 42.47

The formula comes up with 41.10, which means it must be calculating on
the basis of a 30-day term? But A4-A3 = 31. ???