There are 20 days in total so far in September 2025, counting from September 1 to September 20 inclusive. Today's date is September 17, 2025, so counting days up to today yields 17 days so far in the month.

If the question means how many days in the last 20 days from today (backwards), that would be from August 29 to September 17, which is 20 days. Please clarify if needed.