To find the number of days in a month, use this formula:
=DAY(DATE(YEAR(A1),MONTH(A1)+1,0))

Then just do that*500

To be honest with you, the easiest way to calculate charge is this:

=4706.42+(C1-10240)*.9255

The reason why is because EVERY month, even if it only has 28 days, you
will do over 10240 units, so you just want to find out what is the
remainder and multiple it by .9255

Ok. so put it all together in 1 formula:

=4706.42+(DAY(DATE(YEAR(A1),MONTH(A1)+1,0))-10240)*.9255

Not pretty, but it works


--
Bearacade


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