You can calculate it similar to a 11/7 month calculation. Find the equivalent day 6-months earlier. Then add 1 day for each 31 day month that is included in the 6-month timeframe.
Example, you want Nov 15th 2009. Six months earlier is May 15th. There are four 31 day months in that timeframe: May, July, Aug, Oct.
Thus the 180 day mark is May 19th. (May 15th plus 4 days)
You add a day for the 31st day in each month that your timeframe crosses. Thus you count the 1st month if it has 31 days, but not the last month since your reservation is before the 31st of the month.
If February is included, then instead of adding for that month, subtract 2 days (or 1 day for a 29 day month)
Example, you want June 15th 2009. Six months prior is Dec 15th. There are four 31 day months (Dec, Jan, Mar, May) in that timeframe, and one 28 day month, so you call on Dec 17th (Dec 15th plus 4 days and minus 2 days)
Now truthfully, don't you feel better knowing you can calculate 180 days in your head, instead of needing spreadsheets, calculators, or converting to Julian dates????
Of course it helps to have memorized the months. You probably learned it in Grammar school:
30 days hath September, April June and November. All the rest have 31, ....except of course February.
Finally, if you ever see this question on a test....
There are 7 months that have 31 days in them. How may months have 28 days?
The correct answer is ...............
12
