Quick answer
Days until the astronomical start of fall. Enter today's date and hemisphere and the days until fall returns days until, date (UTC) and weekday.
Related tools: Days Until Summer: Days until the astronomical start of summer. Days Until Winter: Days until the astronomical start of winter. Days Until Spring: Days until the astronomical start of spring.
How to use the Days Until Fall
- 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 | 264 |
| Date (UTC) | 2025-09-22 |
| Weekday | Monday |
Example 2
Inputs: Today's date = 2025-06-21; Hemisphere = Northern.
| Result | Value |
|---|---|
| Days until | 93 |
| Date (UTC) | 2025-09-22 |
| Weekday | Monday |
Example 3
Inputs: Today's date = 2026-12-22; Hemisphere = Northern.
| Result | Value |
|---|---|
| Days until | 275 |
| Date (UTC) | 2027-09-23 |
| Weekday | Thursday |
The first line is the headline result (days until). Below it the days Until Fall 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 September equinox
Astronomical fall (autumn) begins at the September equinox, when the Sun's ecliptic longitude is 180° and day and night are close to equal length. Meteorological fall starts on 1 September. This page counts to the equinox.
Equal day and night, almost
The September equinox falls on 22 or 23 September in most years. Day and night are close to equal length on that day everywhere on Earth, and in the southern hemisphere it marks the start of spring.
Start of northern-hemisphere fall (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 | 2026-09-23 | Wednesday |
| 2027-01-01 | 2027-09-23 | Thursday |
| 2028-01-01 | 2028-09-22 | Friday |
| 2029-01-01 | 2029-09-22 | Saturday |
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 Fall 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 Winter](/date-calendar/days-until-winter/) | 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
Is fall the same as autumn?
Yes. Fall is the American word for autumn. The calculator counts to the September equinox, which begins astronomical autumn in the northern hemisphere.
What does the Days Until Fall calculate?
Days until the astronomical start of fall. It returns Days until, Date (UTC) and Weekday.
What formula does the Days Until Fall 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 Fall?
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 Fall is worked out. The choices are Northern and Southern.
What is an example of a days Until Fall result?
With today's date 2025-01-01 and hemisphere Northern, the days until is 264.
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 Winter — Days until the astronomical start of winter.
- 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.