From 1999 to 2023, there are a total of 24 years. To calculate this, subtract the starting year (1999) from the ending year (2023). This will give you the difference in years, which in this case is 24. It is important to note that when counting the number of years between two dates, you include both the starting and ending years in your count.
So, in conclusion, there are 24 years between 1999 and 2023.