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Moon Sighting Hilal Calculator | Predict local crescent visibility

Predicts crescent-moon (hilal) visibility for any date and location using Meeus solar/lunar positions and the Yallop q-criterion — the standard astronomical sighting test.

Last updated: June 2026 · Free · No sign-up required

e.g. +3 Makkah, 0 London, −5 New York (EST). Use your current DST offset.

North positive, south negative.

East positive, west negative.

Results

Enter values above and click Calculate to see your result instantly.

Every Islamic month turns on one question: can the new crescent be seen tonight? This calculator answers it astronomically — it finds your local sunset and moonset, measures the moon’s age since conjunction, its altitude, elongation and crescent width at the best observation time, and grades visibility with the Yallop q-criterion used by professional crescent observers, from zone A (easily visible) to F (impossible).

The positions come from Meeus solar and lunar algorithms validated to a few hundredths of a degree, and the verdict respects the Danjon limit — below 7° elongation no crescent can physically form. Use it to understand why Ramadan or Eid starts when it does in your country, or to plan an actual sighting attempt: it tells you exactly when to look and how long you have before the hilal sets.

Quick reference

Yallop zoneq-valueMeaning
Aq > +0.216Easily visible to the naked eye
B−0.014 < q ≤ +0.216Visible under perfect conditions
C−0.160 < q ≤ −0.014May need optical aid to find first
D−0.232 < q ≤ −0.160Binoculars or telescope only
E/Fq ≤ −0.232Not visible

info Moon Sighting (Hilal) Calculator

Free islamic calculator — enter your numbers and get an instant, accurate result.

info Private by design

Everything runs locally in your browser. No uploads, no accounts, no tracking.

info Works everywhere

Fully responsive and mobile-friendly — calculate on any device, any time.

info Educational

Includes the formula and step-by-step explanation so you understand the math, not just the answer.

Interpretation guide

IndicatorRule of thumb
Moon age 24h: usually sightable somewhere
Lag time 50 min: promising
Elongation (ARCL)< 7° (Danjon limit): physically impossible to see
Negative lagMoon sets before the sun — impossible that evening

lightbulb Worked example

Let's say you are using the Moon Sighting (Hilal) Calculator. Predicts crescent-moon (hilal) visibility for any date and location using Meeus solar/lunar positions and the Yallop q-criterion — the standard astronomical sighting test. Enter the values that match your situation into the input fields and press calculate — using realistic numbers makes the result directly useful for you.

Result: The calculator instantly applies the formula q = (ARCV − (11.8371 − 6.3226W + 0.7319W² − 0.1018W³)) ÷ 10, at best time = sunset + 4⁄9 × lag and returns the result with appropriate precision.

What this means: Read the result in the context of what you are measuring. The step-by-step breakdown lets you confirm the math and understand which input most affects the outcome.

Formula & methodology

Formula: q = (ARCV − (11.8371 − 6.3226W + 0.7319W² − 0.1018W³)) ÷ 10, at best time = sunset + 4⁄9 × lag

  1. Pick the evening and enter latitude, longitude and UTC offset.
  2. The calculator finds local sunset, then moonset, and evaluates the sky at the “best time” = sunset + 4⁄9 of the lag.
  3. Sun and moon positions come from Meeus algorithms (validated to <0.03°); moon age is measured from the true conjunction (new moon).
  4. The Yallop q-test combines crescent altitude (ARCV) and width (W) into zones A–F.

Worked example: Makkah on 18 Feb 2026 (eve of Ramadan 1447): conjunction was 17 Feb 3:02 PM, so the moon is 27.3 hours old at sunset (6:19 PM), sets 55 min later, elongation 14.2°, q = +0.43 → zone A: easily visible — matching the actual Ramadan start on 19 Feb.

Authoritative source: Islamic Relief

Frequently asked questions

How is moon sighting calculated?
Astronomers compute the sun and moon's positions at the “best time” (sunset + 4⁄9 of the moonset lag) and apply the Yallop criterion: crescent altitude versus crescent width. Positive q-values mean naked-eye visibility; below −0.232 the hilal cannot be seen.
What is the youngest moon that can be sighted?
The Moon Sighting (Hilal) Calculator is free, private, and accurate: it runs entirely in your browser (no uploads, no accounts), applies the standard calculation, and explains each step so you can verify the result. Predicts crescent-moon (hilal) visibility for any date and location using Meeus solar/lunar positions and the Yallop q-criterion — the standard astronomical sighting test. There is no limit on usage, and it works on any device.
Why do countries start Islamic months on different days?
Some authorities follow local physical sighting, some accept any global sighting, and Saudi Arabia uses the pre-computed Umm al-Qura calendar. The same astronomy can therefore yield different official start dates — visibility varies by longitude, altitude, and sky conditions, and each authority applies its own criterion. The calculator shows the astronomical data; the official date follows your local authority's method.
What is lag time in moon sighting?
Lag time is the interval between sunset and moonset; a longer lag gives a brighter, more easily visible crescent. The calculator computes the Yallop q-criterion, q = (ARCV − (11.8371 − 6.3226W + 0.7319W² − 0.1018W³)) ÷ 10, evaluated at the best viewing time of sunset + 4⁄9 of the lag, to classify the crescent as easily visible, visible with optical aid, or not visible.
Can the hilal be visible the same evening as the new moon?
Almost never. At conjunction the moon is beside the sun and 0% lit — on 17 Feb 2026 in Makkah it was 3 hours old at sunset and set before the sun (zone F). One evening later it was easily visible (zone A).
What does the Moon Sighting (Hilal) Calculator do?
Predicts crescent-moon (hilal) visibility for any date and location using Meeus solar/lunar positions and the Yallop q-criterion — the standard astronomical sighting test. The calculator takes your inputs, applies the standard calculation, and returns a clear result so you can make an informed decision without doing the math by hand.
What formula does the Moon Sighting (Hilal) Calculator use?
The Moon Sighting (Hilal) Calculator applies the standard formula: q = (ARCV − (11.8371 − 6.3226W + 0.7319W² − 0.1018W³)) ÷ 10, at best time = sunset + 4⁄9 × lag. The tool walks through each step of the calculation so you can verify the numbers yourself.
Is the Moon Sighting (Hilal) Calculator free and private?
Yes — the Moon Sighting (Hilal) Calculator. There is no sign-up, no paywall, no trial, and no limit on how many calculations you can run. CalcaTools covers its costs with non-intrusive display advertising, so the calculator itself never asks for payment or restricts any feature.
How accurate is the Moon Sighting (Hilal) Calculator?
The Moon Sighting (Hilal) Calculator applies the standard formula: q = (ARCV − (11.8371 − 6.3226W + 0.7319W² − 0.1018W³)) ÷ 10, at best time = sunset + 4⁄9 × lag. It is tested against published worked examples before launch and uses native double-precision arithmetic, so results are accurate to typical precision for the values you enter — with no intermediate rounding that could distort the answer.

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