About

Adding 6 calendar months to a date is not the same as adding 180 days. Calendar months vary from 28 to 31 days, so the actual elapsed duration of a 6-month span ranges from 181 to 184 days depending on the start month and leap year status. This distinction matters for contract deadlines, lease expirations, probation periods, and regulatory filings where "6 months" is a legal term tied to calendar arithmetic, not a fixed day count. Miscounting by even one day can void a notice period or trigger a penalty clause.

This calculator applies calendar-month addition with end-of-month overflow correction. If you start on August 31 and add 6 months, the result is February 28 (or 29 in a leap year), not March 3. The tool also reports total calendar days (d), business days excluding weekends, full weeks, and the weekday of the target date. Note: public holidays are jurisdiction-specific and not included. Adjust the result manually for your locale.

Formulas

The target date is computed by calendar-month addition with overflow correction:

D_target = addMonths(D_start, 6)

If the resulting day exceeds the last day of the target month, it is clamped to that month's final day. For example:

addMonths(2024-08-31, 6) → 2025-02-28

Total calendar days between the two dates:

d = D_target − D_start86400000 ms

Business days are computed by iterating each day in the range and excluding those where the weekday index is 0 (Sunday) or 6 (Saturday):

B = d∑i=1

{

1 if weekday(D_start + i) ∉ {0, 6}0 otherwise

Where D_start is the user-selected start date, D_target is the computed end date, d is total calendar days, and B is business days (weekdays only, no holiday adjustment).

Reference Data

Start Month	Days in 6-Month Span (Non-Leap)	Days in 6-Month Span (Leap Year)	End Month	Business Days (Approx.)
January	181	182	July	130
February	184	183	August	131
March	184	184	September	132
April	183	183	October	131
May	184	184	November	131
June	183	183	December	131
July	184	184	January	132
August	184	184	February	131
September	182	183	March	130
October	183	184	April	131
November	182	183	May	130
December	181	182	June	130
Business days exclude Saturdays and Sundays only. Public holidays vary by jurisdiction.

Frequently Asked Questions

Calendar-month addition preserves the day-of-month when possible. January 31 plus 6 months targets July 31, which exists. August 31 plus 6 months targets February 31, which does not exist, so the result is clamped to the last valid day of February - the 28th (or 29th in a leap year). This is known as end-of-month overflow correction and matches the behavior defined in ISO 8601 date arithmetic conventions.

The calculator uses the native Date object which correctly accounts for leap years. A year is a leap year if it is divisible by 4, except for century years which must also be divisible by 400. So adding 6 months from August 31, 2023 yields February 28, 2024 (leap year → 29 would also be valid but the source day 31 clamps to 29). Adding 6 months from August 29, 2023 yields February 29, 2024 exactly.

No. Public holidays are jurisdiction-specific and vary by country, state, and even municipality. The business day count excludes only Saturdays and Sundays. For precise contractual deadlines, subtract your applicable public holidays manually from the reported business day total.

No. Six calendar months span between 181 and 184 days depending on which months are included and whether a leap year is involved. 180 days is an approximation used in some financial contexts (e.g., the 30/360 day-count convention in bond pricing), but it does not match calendar reality. Similarly, 26 weeks equals exactly 182 days, which only coincidentally aligns with certain 6-month spans.

Use the direction toggle provided in the calculator. Selecting "Before" subtracts 6 calendar months from your chosen date using the same overflow-correction logic. For example, 6 months before March 31 yields September 30 of the previous year (since September has only 30 days, the 31st clamps down).

Adding a fixed number of days gives a different result than adding calendar months. Spreadsheet functions like Excel's EDATE(A1, 6) perform true calendar-month addition identical to this tool. Using DATE + 183 is a different operation entirely and will frequently land on a different date. For legal and contractual purposes, "six months" almost always means calendar months, not a fixed day count.