About the Days Until Fall Calculator
This calculator counts the days between any date you choose and the start of fall (autumn), using whichever of the two standard definitions of the season you select, for either the Northern or Southern Hemisphere.
Astronomical fall: the equinox definition
Astronomically, the seasons are defined by Earth's position in its orbit relative to the Sun. Fall begins at the equinox — the moment the Sun crosses the celestial equator and day and night are nearly equal in length everywhere on Earth — and ends at the following solstice, when the Sun reaches its most extreme point in that hemisphere's sky. In the Northern Hemisphere, fall runs from the September equinox (around September 22) to the December solstice (around December 21). In the Southern Hemisphere, the seasons are reversed: fall runs from the March equinox (around March 20) to the June solstice (around June 21). This calculator uses September 22 / December 21 and March 20 / June 21 as the representative dates for these events. Because a calendar year is not an exact whole number of days, the true moment of each equinox and solstice drifts by about six hours per year and resets with the leap-year cycle, so the actual date can fall a day earlier or later than the representative date used here.
Meteorological fall: the calendar-month definition
Meteorologists use a simpler, fixed convention: each season is exactly three calendar months long, grouped by average temperature pattern rather than orbital mechanics. In the Northern Hemisphere, meteorological fall is September 1 through November 30 (91 days); in the Southern Hemisphere it is March 1 through May 31 (92 days). Because these dates never move, meteorological seasons are easier to compare from one year to the next when tracking weather and climate statistics.
How the countdown is calculated
The calculator finds the start and end date of fall for the year of your chosen date, using the selected hemisphere and definition. If your date falls before that year's fall start, it counts the days forward to that start date. If your date already falls within fall, it reports 0 days (you're already in the season) and shows how many days remain until fall ends. If your date is after that year's fall has ended, it rolls forward to the following year's fall start date and counts from there.
How to get the best results
- Pick the hemisphere you actually live in — fall happens at opposite times of year in the Northern and Southern Hemispheres.
- Use the astronomical definition if you care about day length, equinoxes, and solstices; use the meteorological definition if you want clean, fixed calendar-month boundaries for planning or record-keeping.
- Remember the astronomical dates used here are representative averages — check an almanac for the exact hour if you need precision to the day for a specific year.