About Islamic Calendar Conversions

The Hijri calendar conversion algorithms implemented here are based on international astronomical standards. To eliminate observational uncertainties and ensure the most stable mathematical results, the Tabular Islamic Calendar (Mathematical Hijri Calendar) algorithms and Julian Day (JD) constants have been utilized as the primary basis for these calculations.^{1, 2}

Discrepancies of ±1 day may be observed when comparing results with historical sources and manuscripts. Such variances are not errors but stem from the following technical and historical factors:

• Crescent Observation (Ru'yat al-Hilal): Historically, the start of a new month in the Islamic world was based on the physical sighting of the new crescent moon with the naked eye (observational) rather than purely calculated dates.
• Algorithmic Variations: Minor parametric differences may exist between various historical tables, scales, or calculation methods used across different periods and regions.
• Day Transitions: In the Hijri calendar, a new day begins at sunset, which can lead to overlapping dates when synchronized with Gregorian records that transition at midnight.