Quick answer
Days until the astronomical start of winter. Enter today's date and hemisphere and the days until winter returns days until, date (UTC) and weekday.
Related tools: Days Until Summer: Days until the astronomical start of summer. Days Until Fall: Days until the astronomical start of fall. Days Until Spring: Days until the astronomical start of spring.
How to use the Days Until Winter
- Pick today's date.
- Choose hemisphere: Northern and Southern.
- Press Calculate to see the result, and use Reset to start again.
| Input | What to enter | Allowed values |
|---|---|---|
| Today's date | A calendar date | — |
| Hemisphere | Choose one: Northern; Southern | Starts at Northern |
Formula and method
Formula
astronomical seasons begin at the equinoxes and solstices (the Sun's ecliptic longitude is 0°, 90°, 180° and 270°)
IEEE-754 double precision; shown to at most 6 decimal places.
Computed with Meeus's equinox and solstice algorithm. The date shown is the UTC date of the moment the season begins; in time zones far from UTC it can fall on the day before or after. Meteorological seasons (starting on the 1st of March, June, September and December) are different.
Worked examples
These examples are verified: each one is an automated test case that the live calculator must reproduce exactly.
Example 1
Inputs: Today's date = 2025-01-01; Hemisphere = Northern.
| Result | Value |
|---|---|
| Days until | 354 |
| Date (UTC) | 2025-12-21 |
| Weekday | Sunday |
Example 2
Inputs: Today's date = 2025-06-21; Hemisphere = Northern.
| Result | Value |
|---|---|
| Days until | 183 |
| Date (UTC) | 2025-12-21 |
| Weekday | Sunday |
Example 3
Inputs: Today's date = 2026-12-22; Hemisphere = Northern.
| Result | Value |
|---|---|
| Days until | 365 |
| Date (UTC) | 2027-12-22 |
| Weekday | Wednesday |
The first line is the headline result (days until). Below it the days Until Winter lists date (UTC) and weekday, which describe the same case from other angles. IEEE-754 double precision; shown to at most 6 decimal places.
The December solstice
Astronomical winter begins at the December solstice, when the Sun's ecliptic longitude is 270° (northern hemisphere), and it brings the shortest day of the year in the north. Meteorological winter starts on 1 December. Choose the southern hemisphere in the form to count to the June solstice instead.
Shortest day in the north
The December solstice falls on 21 or 22 December in most years. It is the day with the least daylight in the northern hemisphere and the most in the southern, where it marks the start of summer.
Start of northern-hemisphere winter (UTC)
Every figure in this table comes from running this calculator, so it matches what the form returns.
| Counting from | Date (UTC) | Weekday |
|---|---|---|
| 2026-01-01 | 2026-12-21 | Monday |
| 2027-01-01 | 2027-12-22 | Wednesday |
| 2028-01-01 | 2028-12-21 | Thursday |
| 2029-01-01 | 2029-12-21 | Friday |
What happens with invalid input
These messages are produced by the calculator itself, so you know what to fix.
- Today's date: left empty shows "Enter today's date." beside that field and no result.
Choosing between the Days Until Winter and similar calculators
Each row shows what a related calculator on this site asks for and what it returns, so you can pick the one that matches your question.
| Calculator | You enter | It returns |
|---|---|---|
| [Days Until Summer](/date-calendar/days-until-summer/) | today's date and hemisphere | Days until |
| [Days Until Fall](/date-calendar/days-until-fall/) | today's date and hemisphere | Days until |
| [Days Until Spring](/date-calendar/days-until-spring/) | today's date and hemisphere | Days until |
| [Days Until Calculator](/date-calendar/days-until-calculator/) | target date | Days until |
| [Days Until December](/date-calendar/days-until-december/) | Days Until December |
Background: dates and times
Date and time results depend on the conventions a tool uses: whether the end date counts, whether weekends and holidays are skipped, how months of different lengths are handled and whether time zones are applied. This page states its convention, and the worked examples show it.
Dates use the Gregorian calendar and calendar days unless the page says otherwise; check deadlines against the rule in your contract or regulation.
Assumptions and limitations
- Southern-hemisphere seasons are offset by half a year
- The event date is in UTC
If a required value is empty, not a number, or outside its allowed range, the form marks that field with a message and shows no result instead of a misleading number. The automated checks deliberately try invalid entries for today's date to confirm this.
Frequently asked questions
Why does the calculator ask for a hemisphere?
Seasons are opposite in the two hemispheres. Choosing the southern hemisphere makes the page count to the June solstice, the start of southern winter.
What does the Days Until Winter calculate?
Days until the astronomical start of winter. It returns Days until, Date (UTC) and Weekday.
What formula does the Days Until Winter use?
astronomical seasons begin at the equinoxes and solstices (the Sun's ecliptic longitude is 0°, 90°, 180° and 270°). Computed with Meeus's equinox and solstice algorithm.
What do I need to enter in the days Until Winter?
You enter Today's date and Hemisphere.
How is the result rounded or limited?
IEEE-754 double precision; shown to at most 6 decimal places. Southern-hemisphere seasons are offset by half a year.
What are the limits of this calculator?
Southern-hemisphere seasons are offset by half a year. The event date is in UTC.
What does the “Hemisphere” option change?
It sets how the days Until Winter is worked out. The choices are Northern and Southern.
What is an example of a days Until Winter result?
With today's date 2025-01-01 and hemisphere Northern, the days until is 354.
Where does the method come from?
The method follows: Meeus, Astronomical Algorithms, 2nd ed. (1998), chapter 27; validated against JPL DE421 positions via Skyfield for 2020–2035 (maximum difference 1.3 minutes).
Related calculators
- Days Until Summer — Days until the astronomical start of summer.
- Days Until Fall — Days until the astronomical start of fall.
- Days Until Spring — Days until the astronomical start of spring.
- Days Until Calculator — Days remaining until any date (generalizes “days until June 15”, “days until Christmas” and similar pages).
- Days Until December — Days until 1 December.
- Days Until Christmas — Days until Christmas.
Sources
- Meeus, Astronomical Algorithms, 2nd ed. (1998), chapter 27; validated against JPL DE421 positions via Skyfield for 2020–2035 (maximum difference 1.3 minutes)
Content last reviewed 2026-11-04. Formulas and worked examples are checked by automated tests against independently computed values.