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Moon Phase Calculator

Find the moon phase, illumination and lunar age for any date and hemisphere.

Related tools

All Astronomy tools →
Star Visibility CalculatorEstimate how many stars you can see from light pollution, moon phase, clouds and humidity.Sun Position CalculatorCompute the sun's azimuth and elevation for any location, date and time.Sunrise & Sunset CalculatorFind sunrise, sunset, solar noon and day length for any location and date.Tide Time CalculatorEstimate the day's high and low tide times from a known reference tide and pattern.

Open Moon Phase Calculator and you get an answer straight away, with no account to create. You will find it under Astronomy, with Star Visibility Calculator and Sun Position Calculator for the neighbouring cases.

How to use it

  1. Open the tool — no signup or install needed.
  2. Enter your input or adjust the available options.
  3. Get your result instantly, then copy or download it.

Frequently asked questions

What is Moon Phase Calculator?

Find the moon phase, illumination and lunar age for any date and hemisphere.

When would I actually use this?

Planning an observation or a photograph: when the sun sets, what phase the moon is in, and when an equinox or a solstice actually falls this year.

What is the most common mistake?

Treating the equinox as a fixed calendar date. It drifts by up to two days because the tropical year is not a whole number of days, which is the same reason leap years exist.

How is Moon Phase Calculator different from Star Visibility Calculator?

They sit next to each other but answer different questions: Star Visibility Calculator is the one to open when you need it to estimate how many stars you can see from light pollution, moon phase, clouds and humidity. Pick whichever matches what you're starting from — both are free.

Is there a tool for the next step?

Sun Position Calculator is the closest one after this: Compute the sun's azimuth and elevation for any location, date and time.

What else is worth having open alongside it?

Sunrise & Sunset Calculator and Tide Time Calculator — they come up in the same task often enough to be worth a second tab.

Where do the figures come from?

Positions are computed from published ephemeris algorithms (Meeus) including the correction for the Earth's irregular rotation, so results agree with an almanac to well under a minute for the coming decades.

Further reading

All guides →
ExplainerHow Moon Phases Work: Two Months, Eight Shapes, and No ShadowThe phase cycle takes 29.53 days but the orbit takes only 27.32, and the 2.21-day gap is the entire explanation. With the eight phases, their illumination, when each rises and sets, and how they flip south of the equator.ExplainerThe Golden Hour and the Blue Hour Are Angles, Not HoursGolden hour runs from +6° to −4° of solar elevation and blue hour from −4° to −6°, which is why it lasts forty minutes at the equator, over an hour at mid-latitudes, and above 72.6° in June does not happen at all. The thresholds this calculator uses, checked against its own output.ComparisonWhich Fishing Knot Holds Best, and Why Every Published Table DisagreesKnot strength is quoted as a percentage of the line's rated breaking strain, and the percentages in circulation come from tests nobody agrees on. What the calculator on this page really stores, what one peer-reviewed measurement actually found, where a line breaks and why, and how to match a knot to its job.ExplainerSun, Moon and Rising Sign: What Each One Actually IsYour sun sign comes from the date, your moon sign from the Moon's position, your rising sign from the exact time and place. Here is what separates the three and why birth time matters.ExplainerResistors in Series and in Parallel: The Formulas, and the Three Things They Do Not Tell YouSeries adds, parallel adds reciprocals — that part is easy. The parts that catch people: which member dominates the answer, why two 5 % resistors in parallel are still 5 %, and why the smallest resistor in a parallel pair takes the largest share of the power.ExplainerThe Voltage Divider: The Formula Is Trivial, the Assumption Behind It Is NotVout = Vin·R2/(R1+R2) is only true when nothing is connected to the output. Draw current and the voltage collapses, by an amount that follows one exact law. Here is that law, the ten-times rule checked against it, and why a lower-resistance divider costs you power forever.