Calendar Calculator (Month Facts)

Planning shifts, rent periods, payroll or classes often needs month facts – a month can have four or five of a weekday, and between 20 and 23 working days. February has 29 days in leap years.

How to use the Calendar Calculator

1. Month
2. Year
3. Count this weekday

Results update as you type, and every field accepts the units shown in its menu.

How it works

Choose the month and year, and the weekday you want counted.

Tips

• Check whether the end date should be included – event durations usually include it, elapsed time does not.
• Months have 28–31 days, so “one month” is counted by calendar date, not as 30 days.
• Use 24-hour time or set AM/PM carefully when entering clock times.
• Time zones and daylight-saving changes are not applied unless the calculator says so.

Common mistakes to avoid

• Counting a 30-day month when a calendar month is meant (or the reverse).
• Forgetting leap years when counting days across February.
• Mixing decimal hours (7.5 h) with clock time (7:30).

Inputs explained

What each result means

• Days in the month = date([Year], [Month] + 1, 1) – [First day]
• Starts on a = weekday([First day])
• Ends on a = weekday([First day] + [Days in the month] – 1)
• Working days (Mon–Fri) = workdays([First day], [First day] + [Days in the month])
• Weekend days = [Days in the month] – [Working days (Mon–Fri)]
• Number of the chosen weekday = (max(floor((([First day] + [Days in the month] – 1) – (([First day]) + mod(([Count this weekday]) – weekday([First day]), 7)))÷7) + 1, 0))
• Quarter = ceil([Month]÷3)
• ISO week of the 1st = (floor((dayofyear(([First day]) – mod(weekday([First day]) + 6, 7) + 3) – 1)÷7) + 1)
• Day of the year of the 1st = dayofyear([First day])
• Leap year? = isleap([Year])

Example values

How the main result changes when Year changes and everything else stays at the example values above: