I consider 7 days to be a week,
so if I look at 1 January 2019 - 7 January 2019,
I would say that is 7 days.
But often I seen when people are calculating the number of days between two dates or age they use the formula `B1-A1`

where `A1`

is the Start Date/DoB
and `B1`

is the end date or today's date.
This would give 6 for the above example.

I use `(B1-A1)+1`

which gives 7
and for dates of birth I would use `((B1-A1)+1)/365.25`

.
Which is correct?

5days1 January and 7 January. See this. (2) If a person was born on 27 March 1959, on what day did they turn 20? 27 March 1979. Now, ifbetween`B1`

= 27 March 1979 and`A1`

= 27 March 1959, what does your formula say? What does it say for`B1`

= 26 March 1979?