To calculate early finish, early start, early finish etc in days instead of dates use
http://www.timeanddate.com/date/duration.html
to calculate the number of days between two dates. For early and late start, do NOT include the end date. For early and late finish include the end date. If a date lies in the past, treat it exactly the same way. The website will realise that it is in the past and swap the dates for you.