To calculate the interval between occurrences in Excel, you will need to use the following formula:

=B4-A4

where B4 is the cell containing the date of the second occurrence and A4 is the cell containing the date of the first occurrence.

In order to use this formula, you will need to have a list of dates in your Excel spreadsheet. You can either type these in manually, or import them from another source. Once you have your list of dates, simply enter the formula into a blank cell and hit Enter. Excel will automatically calculate the interval between each set of dates.

You can also use this formula to calculate the interval between any two events, not just occurrences. For example, you could use it to calculate the time between someone's birth and death, or between two different milestones in a project.