Sick pay rolling year conundrum

[y_not]

Hi & thanks for reading.

My employee is paid 5 days sick pay in any rolling 30 day period. After he is marked with 5 x "S" in the sheet the 30 day period turns grey indicating that he has no further entitlement. After the 30 days expires, the cells change to white (no colour) until this happens again.

Because my description is pretty rubbish I thought I'd try adding a sample workbook which, hopefully makes a bit more sense.

Thanks in advance for your help.

[p24leclerc]

Not sure it can be done without some VBA programming. Are you in?
In your examples, the employee always takes 5 sick days. But what happens if he/she takes only 2 sick days?
He/she is still entitled to 3 more sick days for a period of 30 days then he/she is back to a 5 sick days bank. Then the cells would not be greyed. Am I right?