6 Month Calculator
This 6 month calculator tells you the exact date six months from today, or six months either side of any date you choose. Pick your start date, set the number of months, and choose whether to count forwards or backwards: the calculator returns the calendar date, the day of the week it lands on, and the number of days and weeks between the two dates. People reach for a tool like this far more often than you might expect. Fixed term tenancies, employment reviews, probation periods and insurance policies are commonly set at six months, as are warrant of fitness cycles for older vehicles, dental checkups and savings milestones, so knowing the precise end date matters. Counting months by hand is easy to get wrong because months are different lengths: six months is never simply 180 days, and a date like the 31st does not exist in every month. The calculator handles those quirks properly, rolling an impossible day back to the last day of the target month, the standard convention used in contracts and calendar software. It also shows you the date the same number of months in the other direction, which is handy for back-dating a start date from a known deadline.
The start date defaults to today in New Zealand. Change any input and the result updates instantly.
Going the other way, 6 months before 16 September 2026 is 16 March 2026.
If the day of the month does not exist in the target month, the result rolls back to the last day of that month.
How it works
The calculator uses standard calendar month arithmetic, the same convention as contracts, spreadsheets and calendar apps. It keeps the day of the month fixed and shifts the month number by the amount you enter, rolling the year over when it passes December. So the 23rd of one month always maps to the 23rd of the target month. The one exception is when that day does not exist: add six months to 31 August and you land in February, which has only 28 days, or 29 in a leap year, so the result clamps to the last day of February. The days between figure is the exact count of calendar days from the start date to the result, and the weeks figure is that count divided by seven, rounded to one decimal place. Because month lengths vary, six months works out to between 181 and 184 days depending on your start point, which is why a months-based deadline and a days-based deadline can differ by several days.
Worked example
Using today as the start date, the calculator begins at 16 September 2026. Adding 6 months keeps the day of the month the same and moves forward 6 calendar months, giving 16 March 2027, which falls on a Tuesday. Counting the individual days between the two dates gives 181 days, which is 25.9 weeks. Going backwards instead, 6 months before 16 September 2026 is 16 March 2026. If you need a different span, change the number of months: the same method applies whether you are adding 3 months for a quarterly review or 18 months for a long fixed term.
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