How this calculator works
Six months is not a fixed number of days, so this page steps on the calendar instead of adding 180 or 182 days. The same day number is kept where the target month has it. If you start on the 31st and the target month has 30 days, the result is the 30th; if you start on August 31 and add six months, February has only 28 or 29 days, so the result is its last day. The step table repeats the same move every six months so a series of review dates can be read at once.
Formula
result = addMonths(start date, +6) when adding, or addMonths(start date, -6) when subtracting, where addMonths clamps the day to the target month's length. net change = O(result) - O(start date).
Worked example
2026-11-01 plus six months is 2027-05-01, a Saturday. Subtracting six months gives 2026-05-01, a Friday. Starting on 2026-08-31 and adding six months lands on 2027-02-28 because 2027 is not a leap year.
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Frequently asked questions
Is six months always 180 days?
No. Six calendar months are 181 to 184 days, depending on which months are covered and whether February 29 falls inside. Stepping by months keeps the date consistent with how contracts and reviews usually define a half year.
What happens if the starting day does not exist six months later?
The result clamps to the last day of the target month. January 31 plus six months, for example, is July 31, while August 31 plus six months is February 28 or 29. This is the same end-of-month rule used by the calendar page.
Does the time of day matter?
No. The inputs are civil dates, so the result is a date with no clock time and no daylight-saving adjustment.
Why not use the month counter?
The month counter measures whole months between two dates that you already have. This page turns six months into a specific future or past date, which is the reverse question.