How is total users given? If it is simply number of accounts that had ever been created, then it would be overestimate because there should be accounts that are inactive for a while, possibly abondoned. There are also users who log in each time with a different new account.
The total users is the plain count of the number of rows found in the users table in SEDE. In Delete old, unloved, users you can find the rules that should be applied to remove users. Due to the backlog of deletions a lot of accounts that once where eligible for deletion are still around, at least on Stack Overflow and will be, forever: When will inactive accounts be deleted?. Lets only keep the established criteria then to decide on what an active user is.
So if we apply the deletion rules to the users table as found in the Stack Exchange Data Explorer we can can determine how many users from the total are to be considered active, by the Stack Exchange definition that is. Here is the query.
When run today you'll find:
# users # users if account deletion rules are applied --------- --------------------------------------------- 7,791,808 3,151,339
See how the 7 million figure is close to the current league numbers (also due to the fact SEDE just updated (on Sunday at 03:00 UTC)):
Notice that it can be important to leave out the inactive/ to be deleted accounts when doing statistics analysis: What is the median reputation level on Stack Overflow?