How does the calculator find the next full moon?

It uses the mean synodic month — 29.530 588 853 days — anchored to a precisely known new moon on 6 January 2000 at 18:14 UTC (Julian date 2451550.1). From any input date it calculates the moon's age within the current cycle and adds the days remaining until the midpoint of the cycle (age ~14.765 days), which is when the Moon is fully illuminated as seen from Earth.

How accurate are the times shown?

The times are typically within 10–20 minutes of published almanac values. The main source of error is that the Moon follows an elliptical orbit, so it moves slightly faster near perigee and slower near apogee. A fully rigorous calculation (as used by NASA) also adds dozens of small perturbation terms; this tool uses the much simpler mean-synodic-month approach, which is accurate enough for planning purposes.

What do the traditional full moon names mean?

The names (Wolf Moon, Snow Moon, Worm Moon, and so on) come from folk traditions recorded by the Old Farmer's Almanac and trace back to Native American, Colonial American and European sources. Each name reflects what was happening in nature during that month — the howling of wolves in January, the first earthworms in March, the sturgeon catches in August. They apply to the Northern Hemisphere; Southern Hemisphere observers experience opposite seasons.

A Blue Moon is the second full moon in a single calendar month (the most common modern definition). Because the synodic month (29.53 days) is shorter than most calendar months (30–31 days), this happens roughly every 2–3 years. The calculator does not label Blue Moons explicitly, but if two full moons fall in the same calendar month in the table, the second is a Blue Moon.

Does the full moon affect sleep or behaviour?

Popular belief says yes, but the scientific evidence is mixed. A widely cited 2013 study in Current Biology found slightly shorter sleep and lower melatonin around full moons, but subsequent large-scale studies have found no consistent effect. The Moon's gravitational influence on humans is far smaller than that of a nearby building. The psychological effect (noticing unusual events and attributing them to the Moon) is well-documented, however.

Why does the moon look bigger near the horizon?

This is purely an optical illusion known as the Moon Illusion. The Moon is actually slightly farther away when it is on the horizon (you are on the surface of the Earth, not its centre), making it marginally smaller in angular size — yet it looks enormous. The brain compares the Moon to foreground objects like trees and buildings and judges it to be much larger than when it is high in a featureless sky.

Next Full Moon Calculator

The full moon has guided calendars, harvests, tides, and folklore for as long as humans have looked up. This tool tells you exactly when the next one arrives — and up to eleven after that — using the same lunar arithmetic astronomers have relied on for centuries, calculated entirely in your browser.

How the formula works

The Moon orbits Earth in an ellipse. The time from one new moon to the next — the synodic month — averages 29.530 588 853 days. That precise figure is the only number the calculator needs, together with a single fixed anchor: a known new moon occurred on 6 January 2000 at 18:14 UTC (Julian date 2451550.1).

Given any date, the tool computes the Moon’s age within its current cycle:

age = (JD_now - JD_ref) mod 29.530 588 853

A full moon occurs at age ≈ 14.765 days (half a synodic month). The days remaining until the next full moon are simply:

days_until_full = 14.765 − age (add one synodic month if the result is negative or zero)

Each subsequent full moon is exactly one synodic month later. The illuminated fraction of the disc at any point follows:

illumination = (1 − cos(2π × age/29.531)) / 2

At a full moon this evaluates to 100%; at a new moon, 0%.

Worked example

Suppose today is 1 June 2026.

Convert to Julian Date: JD ≈ 2461192.5
Days since reference: 2461192.5 − 2451550.1 = 9642.4
Age = 9642.4 mod 29.530 589 ≈ 15.4 days (waxing gibbous)
Days until full: 14.765 − 15.4 = −0.6 → add one synodic month → 28.9 days
Next full moon ≈ 29 June 2026 — the Strawberry Moon

The illumination on that date: (1 − cos(2π × 14.765/29.531)) / 2 ≈ 100%

The table then advances by 29.53 days for each successive entry: Buck Moon (July), Sturgeon Moon (August), and so on.

Traditional moon names

Each full moon carries a folk name rooted in the natural calendar of the Northern Hemisphere:

Month	Name	Origin
January	Wolf Moon	Wolves howled near villages in winter
February	Snow Moon	Heaviest snowfalls of the year
March	Worm Moon	Earthworms emerge as ground thaws
April	Pink Moon	Wild ground phlox blooms (it is pink)
May	Flower Moon	Flowers bloom abundantly
June	Strawberry Moon	Strawberry harvest season
July	Buck Moon	Bucks begin to grow new antlers
August	Sturgeon Moon	Sturgeon most easily caught
September	Harvest Moon	Farmers work late by moonlight
October	Hunter’s Moon	Hunting season begins
November	Beaver Moon	Beavers preparing for winter
December	Cold Moon	Long, cold nights begin

All calculations run client-side — no data is sent anywhere.