Aggregating measure based on dates

Hello,

I have a count of employees working with the slicer on the date. I would like to get a culmative total of employees working based on days selected.

Ex.

# Employees Working = DISTINCTCOUNT(Units[Logon ID])--- this is the measure I used to count employees working.

If I select 1/1/2018 I would have 66 employees working

If I select 1/2/2018 I would have 65 employees working

But if I select the 2 days together I only get 72 employees as opposed to the 131 I want to actually see (1/1/2018 + 1/2/2018)

**If more clarification is needed, please let me know. Thanks in advance!