Count change in excel spreadsheet

[Zaragoza83]

Hi
I would like to count the number of times that I have passed a deadline for a calibration during a year. So far I have made an excel spreadsheet, that looks a bit like below.

Machine number ------interval for calibration ----- Date for calibration ------- latest date for calibration ----------- next calibration--------------status-------
101--------------------- 90----------------------------?????????? ---------------- 18-06-2015 ------------------------- 18-09-2015------------------Deadline passed----------------

I know that I can use the countif function for every time it states "Deadline passed", but when I type in the date for calibration, this will then disappear, and I won't have this for my yearly statistic. This will be due to the date for "next calibration" will change automatically according to the "interval for calibration" (90 days).

Does anybody have any ideas how I can automatically register each "deadline passed" in a spreadsheet, as I want to avoid doing this manually?

 

[jumbledore]

you can just use this formula INT((TODAY()-c2)/90) where C2 contains the date for your first calibration.