Formula that can be used in the Google spreadsheets that will formulate the date, but as in the arithmetic sequence, it has a difference of two

Is it possible that if it is the answer given in the formula? In t It will automatically calculate the date, but the date will be increased by two.

Example: the start date is dec. 22,2018 and the end is jan. 5,2019 can divide these two dates in two, which results in 7, so if the date starts on December 22,2018, the next one will be December. 24,2018, and add again to days until it reaches the final date, which is January. 5,2019.