I'm looking for a formula that will return the amount of interest paid on a
given balance at a given rate, depending on the number of days that the date
shown is from the date invested.

For example, If I invested some money on a date 30 days in the past, Excel,
knowing the date that the money was invested and also knowing the current
date of the system will return the balance of the account and 30 days worth
of interest.

Many thanks

Marcus