Calculating 180 days from any given date can be estimated by simply incrementally increasing the month by six. However, this method will not produce accurate results. For precise calculations, you must determine the exact number of days in each given month. This also means you must consider leap years, which affects the number of days in February. The resulting calculation will give the exact date, 180 days after the given date.
Determine if it is a leap year. This is only required if the start month, or any of the subsequent five months, includes February of a leap year. Any year that evenly divides by four is a leap year, except any year that evenly divides by 100, but not 400. As an example, 1900 is not a leap year, but 2000 is.
Subtract the number of days in the start month by the start date. As an example, if the start date was Feb. 15, 2000, then you would subtract 15 from 29, since it's a leap year. This gives you 14.
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Subtract this difference from 180. In the example, the result is 166.
Subtract the number of days in the next month from the result. Remember that January has 31 days, February has 28 or 29, March has 31, April has 30, May has 31, June has 30, July has 31, August has 31, September has 30, October has 31, November has 30 and December has 31 days. In the example, the result is 135.
Repeat the previous step until the result is less than the number of days in the next month. This next month will be the month in the answer and the remainder will be the day. In the example, subtracting the number of days each month gives the results, 166, 135, 105, 74, 44, 13, respectively. Therefore, your answer is Aug. 13, 2000.