# Calendar Calculator (Month Facts)

URL: https://speedycalculator.com/calculators/everyday-life/calendar/
Last updated: 2026-10-25

> The calendar calculator gives the key facts for any month: how many days it has, which weekday it starts and ends on, the number of working days and weekend days, how many of a chosen weekday it contains, its quarter and ISO week numbers.

## Inputs

- Month
- Year
- Count this weekday

## Results

- Days in the month
- Starts on a
- Ends on a
- Working days (Mon–Fri)
- Weekend days
- Number of the chosen weekday
- Quarter
- ISO week of the 1st
- Day of the year of the 1st
- Leap year?

## Formula

```
Days in month = first day of next month − first day of this month
Working days = Mondays to Fridays in the month
Count of a weekday = number of days in the month that fall on it
```

## Explanation

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

- **Month**
- **Year**
- **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

FieldWhat to enterMonthChoose one: January, February, March, April …YearA numberCount this weekdayChoose one: Sunday, Monday, Tuesday, Wednesday …

### 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:

YearDays in the month1,013311,519.5312,026312,532.5313,039314,05231

## Worked example

Inputs — Month: October; Year: 2,026; Count this weekday: Monday.

Results — **Days in the month = 31**; Starts on a = Thursday; Ends on a = Saturday; Working days (Mon–Fri) = 22; Weekend days = 9; Number of the chosen weekday = 4; Quarter = Q4; ISO week of the 1st = 40; Day of the year of the 1st = 274; Leap year? = No.

## FAQ

**How many working days are in a month?**
Between 20 and 23 for a Monday–Friday week, before holidays.

**Which months have five Fridays?**
Any 31-day month starting on Wednesday, Thursday or Friday, 30-day months starting on Thursday or Friday, and February in a leap year starting on Friday.

**How many days are in each month?**
31: Jan, Mar, May, Jul, Aug, Oct, Dec; 30: Apr, Jun, Sep, Nov; February 28 (29 in leap years).

**What formula does the Calendar Calculator use?**
Days in month = first day of next month − first day of this month.