# Level 3 - Question 46

### Question

Build an event property that tells me the number of days it has been since a user's first day.

*Take Note:*

*And finally, we create the calculation that determines the number of days since a user's first day. In question 44 we assigned a day number to each day (which is the number of days since Jan 1, 1970), in question 45 we built an actor property to determine the first-day number for each user by using the “first” operator and returning day number from question 44. And lastly, we can subtract the two against each other to get the number of days since a user's first day. This can also be used to calculate every day that a user is active since their first day, as we will do in our retention query. *