What is the largest sum of digits in the sum of digits of a five-digit natural number?

The largest five-digit number is 99999, since the next number is 100000 and this is already a six-digit number.
99999 consists of five numbers, five nines, to find the sum, we need to add all five nines:
9 + 9 + 9 + 9 + 9 = 45
or you can find the answer in another way, nine times five, since we have five nines
9 * 5 = 45
Answer: the sum of the digits of a five-digit number is 45