# Days until December 21

Counts the days from today, or any date you choose, to the next December 21, with its day of the week.

- Page: https://www.acalculator.org/days/days-until-december-21
- JSON spec: https://www.acalculator.org/days/days-until-december-21.json
- Version: 5901eb305c83

## Default answer

Example with the default inputs (Count from September 30, 2026) on the example date Wednesday, September 30, 2026: From September 30, 2026, there are 82 days until December 21 on Monday, December 21, 2026.

## Inputs

| Key | Label | Description |
| --- | --- | --- |
| from | Count from | The date to count from. Today, unless you change it. |

## Outputs

| Key | Label | Description |
| --- | --- | --- |
| days | Days until December 21 | Whole days from the start date to the next December 21; 0 on the day itself. |
| date | Date | The next December 21 on or after the start date. |
| weekday | Day of the week | The weekday of that date. |
| weeks | In weeks | The same number of days in weeks and days. |

## Method

Find the first December 21 on or after the start date, then count the days from the start date to it.

## Assumptions

- December 21 comes every year, so the count is never more than 365 days.
- The start date itself is not counted: from the day before December 21, the count is 1; on December 21 itself, it is 0.
- Start dates from January 1, 1900 to December 31, 2400 work for the count to December 21, the range the date field accepts.
- Today is the date on your own device, so the count to December 21 changes at midnight where you are. Dates are whole calendar days, so a daylight-saving change never adds or loses a day.

## Worked examples

1. from = 2027-12-21 gives date = 2027-12-21, days = 0. Source: U.S. Naval Observatory, Leap Years: the Gregorian leap year rule (https://aa.usno.navy.mil/faq/leap_years).
2. from = 2027-01-01 gives date = 2027-12-21, days = 354. Source: U.S. Naval Observatory, Leap Years: the Gregorian leap year rule (https://aa.usno.navy.mil/faq/leap_years).
3. from = 2027-12-22 gives date = 2028-12-21, days = 365. Source: U.S. Naval Observatory, Leap Years: the Gregorian leap year rule (https://aa.usno.navy.mil/faq/leap_years).

## FAQ

### What day of the week is December 21?

Monday, December 21, 2026; Tuesday, December 21, 2027; Thursday, December 21, 2028. The weekday of December 21 moves on one day a year, or two when a February 29 falls between.

### What day of the year is December 21?

December 21 is day 355 of a common year and day 356 of a leap year, such as 2028. Either way, 10 days of the year come after it.

### What season is December 21 in?

In the Northern Hemisphere, December 21 is the first day of winter (the December solstice) in every year from 2026 to 2035; in the Southern Hemisphere, it is summer. Seasons here start on the astronomical equinoxes and solstices, dated in US Eastern Time.

### Is December 21 a US federal holiday?

No. No US federal holiday falls on December 21. The next one in the calendar after December 21 is Christmas Day, which falls on December 25.

### How are the days until December 21 counted?

From the start date to December 21, without counting the start date: from December 20 the count is 1, and on December 21 it is 0. The day after, it moves on to the next December 21: from December 22, 2026, that is December 21, 2027, 364 days away.

## Sources

- 5 U.S.C. 6103 (federal holidays; weekend rule in 6103(b) and Executive Order 11582). Checked against OPM holiday schedules.
- Equinoxes and solstices: Jean Meeus, Astronomical Algorithms (2nd ed., 1998), chapter 27, checked against the US Naval Observatory.