Supermoon Calculator
Find the next supermoon dates and see how close each full moon is to perigee.
| Full Moon Date | Est. Distance | Type |
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How It Works
The calculator finds the next 6 full moons by computing when the lunar phase fraction reaches 0.5, then estimates the Moon's distance from Earth using the lunar anomalistic cycle (approximately 27.55 days — the time between consecutive perigees). A full moon with an estimated distance below ~367,000 km is classified as a Supermoon; one between 367,000 and 375,000 km is "near Supermoon"; anything farther is a regular full moon.
Supermoon Definition
Why the Moon's Distance Varies
The Moon orbits Earth in an ellipse, not a perfect circle. Its closest point (perigee) is approximately 356,500 km from Earth's center; its farthest point (apogee) is about 406,700 km — a difference of roughly 50,000 km or 13%. Because the Moon completes about 13.37 orbits per year but only 12.37 full moons (synodic months) occur per year, the alignment of perigee and full moon slowly cycles through the calendar. A supermoon season — when several consecutive full moons are near perigee — typically lasts 2–4 months.
How Much Larger and Brighter Is a Supermoon?
At the closest perigee full moon, the Moon appears up to 14% larger in diameter and about 30% brighter in area than at its farthest apogee full moon (sometimes called a "Micromoon"). In practice, this is noticeable if you photograph both side-by-side, but is difficult to appreciate with the naked eye without a reference. The "Moon illusion" — where the Moon looks enormous near the horizon — has nothing to do with supermoons; it is a perceptual effect that applies to any moon phase at any distance.
Supermoon and Tides
Supermoons produce slightly stronger-than-normal spring tides (called "perigean spring tides"), typically 2–5 cm higher than average. For most coastal areas this is a minor effect within normal tidal variation. However, when a supermoon spring tide coincides with a storm surge or onshore winds, the combined effect can cause coastal flooding in low-lying areas. This combination is a known coastal hazard that emergency managers track.
Frequently Asked Questions
What makes a Supermoon?
The most common definition: a full moon that occurs when the Moon is within 90% of its closest approach to Earth (perigee) — roughly when the Earth-Moon distance is less than about 367,000 km. The term was coined by astrologer Richard Nolle in 1979; professional astronomers use "perigee full moon" instead.
How often do Supermoons occur?
Typically 3–4 times per year, often occurring in consecutive months when perigee and full moon cycles align. The exact count depends on which definition of "supermoon" is used — stricter definitions (closer to perigee) yield fewer per year.
What is a Micromoon?
A Micromoon (or Apogee Full Moon) is the opposite: a full moon occurring near apogee, when the Moon is farthest from Earth. It appears up to 14% smaller in diameter than a supermoon and about 30% dimmer in total brightness. Micromoons receive much less media attention but are equally interesting from an orbital mechanics perspective.
Can a new moon also be a supermoon?
Yes — any moon phase can coincide with perigee. A new moon at perigee is sometimes called a "Black Supermoon" but is not visible. The term "supermoon" is almost always used exclusively for full moons because those are visible and dramatic.
Are supermoons dangerous?
No — supermoons do not cause earthquakes, volcanic eruptions, or other disasters, despite occasional media claims. The slight increase in gravitational force at perigee is well within the range of normal daily variation. Coastal flooding during extreme perigean spring tides is a real but minor hazard in vulnerable areas.