Time Date Moon Phase Calculator
Moon Phase Calculator works out Phase and Illuminated fraction of the disc from Date (UT), Time (UT) and Your UTC offset (for local dates). The default figures on this page give phase of Full Moon; change any entry and the result, the working and the sources update together.
Your figures
Updates as you typeHow this is worked out
5 steps
- Julian Day for 2024-01-25 12 h UT is 2460335.
- Apparent elongation of the Moon from the Sun: 177.2341 degrees (0 = new, 180 = full), so the Moon is waxing.
- Illuminated fraction = (1 + cos(phase angle)) / 2 = 99.763%.
- Previous new moon 2024-01-11 11:58 UT, so the Moon is 14.001 days old; the next new moon is 2024-02-09 23:00 UT, making this lunation 29.4596 days rather than the 29.5306-day average.
- Next full moon: 2024-01-25 17:55 UT.
Its 4 worked examples are re-run on every release, last on 15 September 2026. What changed
Sources and references
3 sources
What the Moon Phase Calculator calculates
The Moon’s phase at a date and time in Universal Time: the named phase, the illuminated fraction of the disc, the Moon’s age in days since the previous new moon, and the exact instants of the surrounding new and full moons. Phase is computed from the Sun-Moon elongation (0 degrees new, 180 full), not from a fixed 29.53-day cycle, because individual lunations vary by more than half a day.
How to use this Moon Phase Calculator
Enter Date (UT), Time (UT) and Your UTC offset (for local dates). Phase updates as you type, and “Use a worked example” loads checked figures you can adjust. Change one figure at a time to see what drives the result.
How the result is worked out
Open “How this is worked out” beside the result for the step-by-step calculation behind Phase, Illuminated fraction of the disc and Sun-Moon elongation.
The method follows Jean Meeus, Astronomical Algorithms, 2nd edition, chapters 25 (solar coordinates), 47 (position of the Moon) and 48 (illuminated fraction), US Naval Observatory, Astronomical Applications Department: phases of the Moon and IERS / Espenak-Meeus Delta T polynomials.
The new moon of 11 January 2024 example
With Date (UT): 2024-01-11, Time (UT): 11:57, the calculator returns Phase: New Moon, Elongation from new moon (-180 to 180): 0. This example is checked against an independent source in the test suite.
What you can compare
Change one input at a time to see how it affects Phase, Illuminated fraction of the disc and Sun-Moon elongation. The inputs you can vary are Date (UT), Time (UT) and Your UTC offset (for local dates).
Understanding Phase, Illuminated fraction of the disc and Sun-Moon elongation
For entertainment and cultural interest. Astrology and numerology are traditional practices with no scientific basis for predicting events or describing a person; do not use them for health, financial or legal decisions.
Results are general information, not financial, tax, legal, medical or engineering advice. Check any decision that matters with a qualified professional.
See something wrong? Report a problem with this calculator
Frequently asked questions
How do I calculate my moon phase?
The Moon’s phase at a date and time in Universal Time: the named phase, the illuminated fraction of the disc, the Moon’s age in days since the previous new moon. Open “How this is worked out” beside the result to see each step for your own figures.
Which moon phase is the luckiest?
The Moon’s phase at a date and time in Universal Time: the named phase, the illuminated fraction of the disc, the Moon’s age in days since the previous new moon. Put your own figures in above and the working updates beside the result. For scale, the default figures on this page give Full Moon.
What is my current moon phase?
The Moon’s phase at a date and time in Universal Time: the named phase, the illuminated fraction of the disc, the Moon’s age in days since the previous new moon. On this page it is computed from Date (UT), Time (UT) and Your UTC offset (for local dates) and shown as Phase, Illuminated fraction of the disc and Sun-Moon elongation.
What moon phase is 99%?
It needs Date (UT), Time (UT) and Your UTC offset (for local dates). Nothing else is required, and the figures stay in your browser.
What information do I need for the Moon Phase Calculator?
You need Date (UT), Time (UT) and Your UTC offset (for local dates). The page opens with default figures that give phase of Full Moon, so you can see the scale before entering your own.
What does this Moon Phase Calculator show?
It shows Phase, Illuminated fraction of the disc, Sun-Moon elongation, Elongation from new moon (-180 to 180), Age since the last new moon, Waxing or waning, Previous new moon (UT) and Previous new moon time (UT), with the working and any warnings for your entries.