How many days are in December?
December has 31 days in the Gregorian calendar. It is the twelfth and final month of the year, following November and coming before January. Its length stays the same in common years and leap years.
The month begins on December 1 and ends on December 31. Because December always contains 31 calendar dates, it is useful for planning deadlines, holiday schedules, billing cycles, travel, work periods, and end-of-year events.
December’s day count does not change when the year is a leap year. Leap years add one day to February, increasing that month from 28 to 29 days, while December remains a 31-day month.
December always has 31 days
The Gregorian calendar assigns 31 days to December every year. This includes years such as 2000, 2024, 2028, and 2050, regardless of whether the year has 365 or 366 total days.
December is one of seven months with 31 days. The other months are January, March, May, July, August, and October. April, June, September, and November have 30 days, while February has either 28 or 29.
This consistent length makes December easy to use in date calculations. A period beginning on December 1 and ending on December 31 covers the entire month and includes 31 calendar days.
Leap years do not add a December date
A leap year contains 366 days instead of the usual 365. The extra day is placed in February because the calendar adjustment is made early in the year. December still ends on the 31st, and there is never a December 32.
For a concise explanation of the wider calendar pattern, see how leap years occur. The standard rule is that a year divisible by four is usually a leap year, except for century years that are not divisible by 400.
This means 2000 was a leap year, while 2100 will not be one. These rules affect the total number of days in the year and the weekdays associated with later dates, but they do not alter December’s 31-day count.
December in the annual calendar
December is the final month in both common and leap years. In a common year, December 1 is the 335th day, and December 31 is the 365th day. In a leap year, December 1 is the 336th day, and December 31 is the 366th day.
The difference comes from the extra February date. After February 29 has passed, every later date in a leap year has an ordinal day number one greater than it would have in a common year.
| Calendar detail | Common year | Leap year |
|---|---|---|
| Total days in the year | 365 | 366 |
| Days in December | 31 | 31 |
| December 1 | 335th day | 336th day |
| December 31 | 365th day | 366th day |
| Days after December 31 | January 1 follows | January 1 follows |
Weekdays and December date patterns
Although the number of days is fixed, the weekday for each December date changes from year to year. For example, December 1 may fall on a Monday in one year and a Wednesday in another. The weekday of December 31 also depends on the year’s starting weekday and whether February contained 29 days.
A 31-day month spans four full weeks plus three additional days. As a result, three weekdays occur five times during December, while the other four weekdays occur four times. Which weekdays receive five occurrences depends on the day of the week on which December 1 falls.
Leap years influence future weekday patterns because the extra February day shifts dates after February by one weekday. A December date in a leap year may therefore fall on a different weekday than the same numbered date in the previous or following common year.
Planning dates across December
When counting a deadline or event period, distinguish between calendar days and business days. December has 31 calendar days, but the number of working days can be lower because Saturdays, Sundays, public holidays, personal leave, and business closures may be excluded.
A date range from December 1 through December 31 is inclusive and contains 31 days. If the first or last date is left out, the count changes. For instance, the interval from December 1 up to, but not including, December 31 contains 30 days.
The final week of December can also cross into January when planning a countdown. A countdown to January 1 should identify whether December 31 is included, since inclusive and exclusive counting produce different results. For dates far in the future, a year-specific calendar lookup can prevent weekday and leap-year errors.
Practical ways to use the day count
December’s fixed length is helpful for routine calculations, but exact date rules still matter. Use these practices when working with month totals, schedules, or countdowns:
- Count December 1 through December 31 inclusively when measuring the full month.
- Keep calendar-day totals separate from business-day totals.
- Check whether a date range crosses into January.
- Remember that leap years change February and annual totals, not December.
- Verify weekdays for a specific year before setting an appointment or deadline.
A year with a 366-day orbit is a useful way to think about why calendar systems sometimes need an adjustment, although astronomical years and civil calendar years are not identical. The explanation of 366-day calendar years provides additional context for comparing annual day counts.
Check your December dates quickly
For a quick reference, December contains 31 days every year under the Gregorian calendar. Use a calendar calculator to identify the weekday of a particular date, count elapsed days, calculate working days, or create a countdown to the end of the year. Look up the specific year when accuracy matters, then use December 31 as the reliable final date.