Count Days in Between

Hi, do you guys have an idea on how to count day in between 1st Jan 2021 until today.
I need to count the utilization or percentage of usage like 1st Jan 2021 until today is 265 days.
Let say row no 1 that I wrote using Red Pen below is 0 as Start and End Date is on 2020.

Let say item 2 that I wrote is 28 December 2020 to end date 27 January 2021.
So it will become 27 days since it will be count starting of first January 2021.

And Item 3 is two day from 8 Jan 2021 to 10 Jan 2021.

Another example is as below :
Item 4 is from 1 February 2020 to 28 February 2023 . So it will become 265 days.
it will be count from 1 jan 2021 until today.