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Printable moon phase calendar for any month

Pick a month and print a moon calendar at the exact size of the paper in your tray. Every disc is drawn from that day's computed illuminated fraction — so a thin crescent and a fat one are genuinely different shapes, not the same stock glyph twice. Generated in your browser as vector geometry, with no watermarks, no sign-ups, and nothing uploaded.

Sheet— Days— Full moon— New moon—

How this generator works

Each day on the sheet is asked one question: what fraction of the Moon's disc is lit at midnight UTC? That number comes from the positions of the Sun and Moon computed with the standard Meeus series, corrected for the difference between clock time and the uniform time the series is written in — a gap of roughly 75 seconds today, which sounds negligible and moves the Moon about 41 arcseconds. The primary phases are found as instants rather than looked up, so the sheet knows the full moon happens at a particular moment on a particular day, not merely that a day is "around full".

The drawing then carries that number rather than illustrating it. The lit region of each disc is bounded by a semicircle on one side and a semi-ellipse on the other, and the ellipse's width is the day's own illuminated fraction: it is widest at new and full, and collapses to a straight line at exactly half. The consequence is that the area actually inked equals the fraction times the area of the disc — an identity this site's test suite measures on the emitted drawing, because a picture that disagrees with the number it was drawn from is invisible to every other kind of check. Waxing moons are lit on the right, which is the northern-hemisphere view and is stated on the sheet, because it genuinely mirrors below the equator.

The limits are worth stating plainly. A phase is a moment and a calendar cell is a day, so any moon calendar has to choose a time zone before it can say "the full moon is on the 4th"; this one chooses 00:00 UTC and prints that in the footer instead of leaving you to guess. The range is 1800 to 2150, and clock times toward the far end carry genuine uncertainty because the slowing of Earth's rotation is measured, not predicted — reputable sources already differ by minutes about the year 2100, though the calendar day is not in doubt. Percent-lit labels and phase names only appear when the cells are tall enough to hold them without colliding with the row below, so a landscape sheet with six week rows will drop them rather than overprint. And the sheet is a wall calendar, not an ephemeris: if you need the phase at a specific local minute, that is a different instrument than this one.

Frequently asked questions

How accurate are the phases on this sheet?
The phase of each day is computed from the positions of the Sun and Moon using the standard Meeus series, with the Espenak and Meeus correction for the slowing of Earth's rotation. The same engine's phase instants agree with the US Naval Observatory's published table to under a minute and a half across every era where Earth's rotation has actually been measured. What it does not do is the shortcut most printables use — counting days since a known new moon and dividing by 29.53 — which drifts by up to about fourteen hours and names the wrong day several times a year.
Why does my sheet show a full moon on a different day than another calendar?
Almost always the time zone. A phase instant is a moment, not a day, and a full moon at 00:40 UTC on the 5th is still the evening of the 4th in New York. Every moon calendar has to pick a zone, and most of them never say which. This sheet computes at 00:00 UTC and prints that basis in the footer, so you can tell what convention produced it. If you need the phase for a specific local moment rather than a whole day, that is a different question than a wall calendar answers.
Can I print a blank moon calendar for tracking the moon myself?
Yes — set Style to "Blank circles to fill in" and every day gets an empty circle instead of a drawn phase. That is the version science teachers use for a month-long observation exercise, where the point is that the student draws what they actually see. The dates, weekday columns and week rows are still computed, so the sheet is correct for the month you picked; only the discs are left empty.
Which years can it generate, and why is the disc shape different from other calendars?
Any month from 1800 to 2150, which is the range the underlying astronomy is trusted over; clock times past about 2050 carry real uncertainty because the slowing of Earth's rotation is measured rather than predicted, though the calendar day stays right. The disc shape differs because most printables pick one of eight stock glyphs, so every crescent looks the same. Here the terminator is an ellipse whose width comes from that day's illuminated fraction, so a 3 percent crescent and a 47 percent crescent are visibly different shapes — the drawing carries the number rather than illustrating it.
Is anything uploaded or stored?
No. The sheet is generated as vector geometry inside this page, printed through your browser's own dialog, and never exists anywhere but on your device. No account, no watermark, no stored settings — close the tab and it's gone.

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