I have a spreadsheet with a date column. When I enter 1/1/2018 the cell returns 43101. This must be the number of days from 1/1/1900.
When I calculate the entered date from this number of days the result is 1/3/2018. I use this function:
var
days = 43101
var
date =
new
Date(1900, 0, 1);
date.setDate(date.getDate() + days);
Here you can find an example: http://dojo.telerik.com/aNuXAkuB
The Days function in Excel returns 43100 for the number of days between 1/1/1900 and 1/1/2018.