Math Equation

Let say its counted from the year 2021 which labeled as a year 1.
Now current balance leave to be cleared is 33 days. Each year have to be clear minimum 10 days.
I need the number of balance leave to be cleared.
For current cases, 2021 is 10, 2022 is 10, 2023 is 10 and 2024 is 3.
Like for now, current year is 2022. It should be deduct 20 days already.
In my mind, I will using if-then column if “B/F <2021” column is more than 10.