Moon Phase Calculator
Pick any date — past, present, or years into the future — and see what moon phase it falls on: name, illumination, moon age, and the next full and new moons from there. Works the same for any location on Earth, since the moon's phase doesn't depend on where you're standing.
Why do we have moon phases?
The moon doesn't produce its own light — the phase you see is just how much of its sunlit half is facing Earth at that moment. As the moon orbits Earth roughly once a month, that angle changes continuously, cycling through new moon (sunlit side facing away from us), full moon (sunlit side facing us), and everything in between.
One full cycle, new moon to new moon, is called a synodic month and averages about 29.53 days — slightly longer than the moon's actual 27.3-day orbit, because Earth is also moving around the sun in the meantime.
The eight moon phases
| New Moon | ~0% illuminated |
| Waxing Crescent | growing, 1–49% |
| First Quarter | ~50%, growing |
| Waxing Gibbous | growing, 51–99% |
| Full Moon | ~100% illuminated |
| Waning Gibbous | shrinking, 51–99% |
| Last Quarter | ~50%, shrinking |
| Waning Crescent | shrinking, 1–49% |
"Waxing" means growing more illuminated night to night; "waning" means shrinking. Once you know which half you're in, the phase name follows from the percentage.
Frequently asked questions
Is the moon phase the same everywhere on Earth?
Yes. Everyone on Earth sees the same phase on the same date — what changes by location is when the moon rises and sets, and (in the southern hemisphere) which side looks lit, not the phase or illumination percentage itself.
How accurate is this calculator?
It's accurate to within a few hours for any date, which is plenty for planning or curiosity, but it uses a simplified model (a fixed 29.53-day average cycle) rather than full orbital mechanics, so it isn't intended for professional or scientific use.
How often is there a full moon?
About every 29.53 days, the length of one synodic month. Most calendar months contain exactly one full moon; occasionally a month contains two, and the second is popularly (if inaccurately, by the original definition) called a "blue moon."
What's the difference between waxing and waning?
Waxing means the illuminated portion is growing night to night, on its way from new moon to full moon. Waning means it's shrinking, on its way from full moon back to new moon.
Why isn't the synodic month exactly 29.5 days?
29.530588853 days is an average — the moon's actual orbit is elliptical and Earth's orbital speed varies too, so any individual cycle can run several hours shorter or longer than the average. This calculator uses the average, which is why it's accurate to hours rather than minutes.