Well you can start by changing 180 days into months and some days. and then add them to that date.

180 days divide it by the number of days in a month. (30 or 31). So 180/30 is 6. that means that its 6, 30 days month but we know that no all month have the same number of days. half of the month have 31. so from 6 month you have to take three days off. so that comes out to be 5 months and 27 days.