calculating depreciation

Hello:
I'm trying to figure out what combinations of formulas could be used to make this work. I have attached a sample spreadsheet with the logical steps that I need it to take.

I'm hoping that someone can help.

Thank you!

I think I can help, but I don't understand what you mean when you say that you need to calculate the percentage of days.

Some things to try
=date(2007,6,31)-b3 'will give you the number of days between the purchase date and the end of the quarter.

From there it's just math... be carefull with parenthasis!