Problem:

We want to create a formula to calculate the number of days between each pair of dates in columns A & B, but the formula is never to return a negative value.
Empty cells in column A are to be considered the first day of the year, and empty cells in column B are to be considered the last day of the year.

Solution:

Use the MAX, MIN, and DATE functions as shown in the following formula:
=MIN(B2,DATE(2005,12,31))-MAX(A2,DATE(2005,1,1))