# Days until December 31

Counts the days from today, or any date you choose, to the next December 31, with its day of the week.

- Page: https://www.acalculator.org/days/days-until-december-31
- JSON spec: https://www.acalculator.org/days/days-until-december-31.json
- Version: 3ede3f2dc2db

## 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 92 days until December 31 on Thursday, December 31, 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 31 | Whole days from the start date to the next December 31; 0 on the day itself. |
| date | Date | The next December 31 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 31 on or after the start date, then count the days from the start date to it.

## Assumptions

- December 31 comes every year, so the count is never more than 365 days.
- The start date itself is not counted: from the day before December 31, the count is 1; on December 31 itself, it is 0.
- Start dates from January 1, 1900 to December 31, 2400 work for the count to December 31, the range the date field accepts.
- Today is the date on your own device, so the count to December 31 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 = 2027-12-31 gives date = 2027-12-31, 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 = 2027-12-31, days = 364. Source: U.S. Naval Observatory, Leap Years: the Gregorian leap year rule (https://aa.usno.navy.mil/faq/leap_years).
3. from = 2028-01-01 gives date = 2028-12-31, 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 31?

Thursday, December 31, 2026; Friday, December 31, 2027; Sunday, December 31, 2028. The weekday of December 31 moves on one day a year, or two when a February 29 falls between.

### What day of the year is December 31?

December 31 is the last day of the year: day 365 of a common year and day 366 of a leap year, such as 2028.

### What season is December 31 in?

In the Northern Hemisphere, December 31 is in winter 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 31 a US federal holiday?

In some years. December 31 is the federal day off for New Year's Day when January 1 falls on a Saturday, as on Friday, December 31, 2027.

### How are the days until December 31 counted?

From the start date to December 31, without counting the start date: from December 30 the count is 1, and on December 31 it is 0. The day after, it moves on to the next December 31: from January 1, 2027, that is December 31, 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.