I've created an excel document to track attendance occurrences. The occurrences are added to the excel tab with the start date in one column and the end date in another. I have another column that has the single occurrence associated with the date. Each row is a unique occurrence for a particular agent by name. On a separate tab, I have a calendar with a drop-down for the agent's name. When the agent's name is selected it shows on the calendar what days the agent received an occurrence. Below is a count of how many occurrences the agent has. I want this occurrence count to count the occurrences based on a 12-month rolling calendar. Once the 12 months have passed it should no longer be counted as an occurrence. This is the formula I'm currently using to calculate the occurrences.