To find a relative date 100 days in the future from May 13th, you can use a simple manual calculation method. Start by adding 100 days to May 13th. Since May has 31 days, subtract 13 from 100, leaving you with 87 days. Moving forward, June has 30 days, so subtracting 87 days would give you the date June 19th. Therefore, the relative date 100 days in the future from May 13th is June 19th.