DateDelta

Moon Phase Calculator

See which of the 8 lunar phases the Moon is in on any given date, past or future.

Date

Moon phase

Waning Crescent

16% illuminated

Days into the lunar cycle: 25.7

What you entered

Date: 2026-09-08

1
Days since the reference new moon (Jan 6, 2000)
(date − reference) ÷ 1 day, mod synodic month= 25.6765 days into the cycle
2
Match against the 8 standard moon phases
25.6765 ÷ 29.5306 × 8= Waning Crescent
3
Approximate illumination
(1 − cos(2π × cycle position)) ÷ 2= 15.8897%

Result

Moon phase: Waning Crescent

On 2026-09-08, the Moon is in its Waning Crescent phase, roughly 16% illuminated — this is an approximation based on the average 29.53-day lunar cycle, accurate to within about a day.

Moon phases through January 2026

Phase, illuminated fraction and age in days at weekly intervals, showing a full cycle.

Date	Phase	Illumination	Age (days)
1 January 2026	Waxing Gibbous	0.91	11.92
8 January 2026	Waning Gibbous	0.82	18.92
15 January 2026	Waning Crescent	0.14	25.92
22 January 2026	Waxing Crescent	0.12	3.39
1 February 2026	Full Moon	0.98	13.39

The synodic month - new moon to new moon - is about 29.53 days, which is why the age column wraps between the 15 and 22 January rows. Illumination is not linear in age: the moon spends longer looking nearly full or nearly new than the halfway phases, because the terminator sweeps across a sphere. Waxing means growing and waning shrinking, and in the northern hemisphere a waxing moon is lit on the right, reversed in the southern hemisphere. This is a mathematical model, so it can differ from an ephemeris by a few hours.

Why this is an approximation

The Moon's orbit isn't perfectly circular or constant-speed, so the true time between new moons varies by several hours around the 29.53-day average used here — this calculator is accurate to within roughly a day, which is precise enough for general reference but not exact astronomical prediction.

What illumination percentage means

0% illumination is a New Moon (fully dark), 100% is a Full Moon (fully lit) — the percentage describes how much of the visible lunar disk appears lit from Earth's perspective on that date.

Frequently asked questions

I'm planning an outdoor event on October 15, 2025 — will the moon be bright enough to see by?

Enter the date to check. A moon above ~50% illumination (waxing gibbous to full) provides meaningful ambient light outdoors. Below 25% (crescent phases) it will be quite dark. The full moon is typically the brightest night of the month.

How long is a complete lunar cycle?

The average synodic month (new moon to new moon) is 29.53 days, but individual cycles vary from about 29.2 to 29.8 days because the Moon's orbit is elliptical. This calculator uses the 29.53-day average, making it accurate to within roughly a day.

What's the difference between waxing and waning?

Waxing means the lit portion is growing (new moon → full moon), waning means it's shrinking (full moon → new moon). The 8 phases in order: New → Waxing Crescent → First Quarter → Waxing Gibbous → Full → Waning Gibbous → Last Quarter → Waning Crescent → New.

How is this different from the Zodiac Sign Calculator?

The Zodiac Sign Calculator identifies which constellation the Sun occupied on your birth date (your star sign). This calculator tracks the Moon's illumination phase on any date — they measure completely different things, though both are based on astronomical cycles.