# What is the moon phase on my date?

Shows the Moon’s phase, illuminated percent and age on any date and time from 1900 to 2149, with the dates and times of the next new moon, first quarter, full moon and last quarter.

- Page: https://www.acalculator.org/physics/moon-phase-calculator
- JSON spec: https://www.acalculator.org/physics/moon-phase-calculator.json
- Version: bca1af72f8ef

## Default answer

Example with the default inputs (Date October 2, 2026, Local time 12:00, UTC offset (hours) 0) on the example date Friday, October 2, 2026: Moon phase on October 2, 2026: Waning gibbous, 62.3% lit. Next full moon: 2026-10-26 04:12.

## Inputs

| Key | Label | Description |
| --- | --- | --- |
| date | Date | The local date to look at. |
| time | Local time | The local time of day; the phase changes through the day. |
| utc | UTC offset (hours) | Your time zone’s offset from UTC on that date: −5 for New York in winter, −4 in summer, 1 for Paris in winter. |

## Outputs

| Key | Label | Description |
| --- | --- | --- |
| phase | Moon phase | The phase name on that local date. |
| illuminated | Illuminated | The share of the Moon’s disk lit by the Sun, as seen from Earth. |
| age | Moon age (days) | Days since the last new moon. |
| trend | Waxing or waning | Waxing from new to full, waning from full to new. |
| lastNew | Last new moon | Local date and time of the last new moon. |
| nextFirst | Next first quarter | Local date and time of the next first quarter. |
| nextFull | Next full moon | Local date and time of the next full moon. |
| nextLast | Next last quarter | Local date and time of the next last quarter. |
| nextNew | Next new moon | Local date and time of the next new moon. |

## Method

Phase times: Meeus ch. 49 (mean phase plus periodic and planetary terms), converted from TD to UT with NASA’s ΔT polynomials. Illuminated fraction k = (1 + cos i) ÷ 2 with the phase angle i from Meeus eq. 48.4.

## Assumptions

- Times are to the nearest minute; Meeus gives phase times to within about a minute of the full theory for 1900 to 2100.
- The phase name is that of a new moon, quarter or full moon that falls on your local date; otherwise crescent (under 50% lit) or gibbous (50% or more), waxing or waning.
- Illumination is for the Earth’s centre and the time you type.

## Worked examples

1. date = 2026-06-29, time = 23:56, utc = 0 gives phase = Full moon, lastNew = 2026-06-15 02:54, nextLast = 2026-07-07 19:29, nextNew = 2026-07-14 09:43. Source: Meeus (1998), Astronomical Algorithms, 2nd ed., ch. 49; U.S. Naval Observatory, Phases of the Moon 2026, the check (new moon June 15 02:54, last quarter July 7 19:29, new moon July 14 09:43 UT). https://aa.usno.navy.mil/data/MoonPhases.
2. date = 2026-10-01, time = 12:00, utc = 0 gives phase = Waning gibbous, trend = Waning, lastNew = 2026-09-11 03:27, nextLast = 2026-10-03 13:25, nextNew = 2026-10-10 15:50, nextFull = 2026-10-26 04:12. Source: Meeus (1998), Astronomical Algorithms, 2nd ed., ch. 49; U.S. Naval Observatory, Phases of the Moon 2026, the check (new moon Sept 11 03:27, last quarter Oct 3 13:25, new moon Oct 10 15:50, full moon Oct 26 04:12 UT). https://aa.usno.navy.mil/data/MoonPhases.
3. date = 2026-10-10, time = 09:00, utc = -5 gives phase = New moon, lastNew = 2026-09-10 22:27, nextNew = 2026-10-10 10:50, nextFull = 2026-10-25 23:12. Source: Meeus (1998), Astronomical Algorithms, 2nd ed., ch. 49; U.S. Naval Observatory, Phases of the Moon 2026, the check (new moon Sept 11 03:27, new moon Oct 10 15:50, full moon Oct 26 04:12 UT). https://aa.usno.navy.mil/data/MoonPhases.

## FAQ

### What phase is the moon in today?

The page opens on today’s date at 12:00 UTC. Type your local time and your UTC offset (−5 for New York in winter, −4 in summer) to get the phase where you are.

### What are the eight moon phases?

New moon, waxing crescent, first quarter, waxing gibbous, full moon, waning gibbous, last quarter and waning crescent. New, first quarter, full and last quarter are instants; the page names a day after one of them when it falls on that local date, and uses crescent or gibbous in between.

### How is the moon phase calculated?

The page uses Jean Meeus’s Astronomical Algorithms: chapter 49 gives the time of each new moon, quarter and full moon from a mean lunation plus about 40 correction terms, and chapter 48 gives the lit fraction from the Sun-Moon angle. NASA’s ΔT polynomials turn the result into Universal Time.

### How accurate are the times?

Within a minute or two of the U.S. Naval Observatory for 1900 to 2100: every 2026 phase on the page matches the USNO table to within 1 minute. Times are rounded to the nearest minute.

### How long is a lunar cycle?

A synodic month, from one new moon to the next, averages 29.530588861 days (Meeus), about 29 days 12 hours 44 minutes. Single cycles vary by several hours because the Moon’s orbit is an ellipse.

### What was the moon phase on the day I was born?

Type your birth date, the time if you know it, and the UTC offset where you were born. Any date from 1900 to 2149 works. Without a time, the page uses 12:00.

## Sources

- Jean Meeus, Astronomical Algorithms, 2nd ed. (Willmann-Bell, 1998), chapter 47 (D, M, M′), chapter 48 (illuminated fraction, eq. 48.4) and chapter 49 (phases of the Moon; examples 49.a and 49.b).
- NASA Goddard Space Flight Center (F. Espenak), Polynomial Expressions for Delta T (ΔT), 1900 to 2150. https://eclipse.gsfc.nasa.gov/SEhelp/deltatpoly2004.html (retrieved 2026-10-01)
- U.S. Naval Observatory, Astronomical Applications Department, Phases of the Moon (UT), the check for 2026. https://aa.usno.navy.mil/data/MoonPhases (retrieved 2026-10-01)