Calculating Due days using a formula column and Date column

Hi All,
I’m new to I have been trying to calculate difference between 2 dates. I’m using “DAYS” function for this. I have two columns

  1. Task 1 Original date: which is a formula column generating date.
  2. Task 1 Done date: Which is a date column and user will input the date.

Formula using:
DAYS({Task 1 Original date}, {Task 1 Done date})

Using above formula I’m getting error. Is there a way I can calculate Due days using formula and date columns.