Muslim holidays and significant events are celebrated annually according to the Islamic calendar-Hijri, the chronology of which is conducted from the date of migration (Hijra) of the Prophet Muhammad from Mecca to Medina in 622. Due to the fact that the Muslim lunar calendar consists of 12 lunar months and lasts mainly 354 days, which is 10 or 11 days shorter than the solar year, the days of Muslim religious holidays are shifted each year relative to the Gregorian calendar.

Thus, Muslim holidays and significant events in 2021, according to astronomical calculations, fall on the following dates:

- 18-19 February - Laylat ar-Raghaib (Marriage of the Prophet's parents);
- 10-11 March - Laylat al-Isra wal-Mi'raj (Transfer of the Prophet from Mecca to Jerusalem and his ascension);
- 27-28th March - Laylat al-Baraat (Night of Purification from Sins);
- 13th of April -The beginning of the month of Ramadan – The first day of mandatory fasting;
- 8-9th of May - Laylat al-Qadr (Night of Predestination);
- 13th of May - Eid al-Fitr (Eid al-Fitr, the Feast of Thanksgiving);
- 19th of July - the Day of Araf;
- 20-22nd of July - Eid al-Adha (Eid al-Adha, the Feast of Sacrifice);
- 9th of August-Ras al-Sana'a (beginning of the New Year 1443 AH);
- 18th of August - Ashura Day (Day of Remembrance of the Messengers and Prophets);
- 17-18th of October - Mawlid al-Nabi (the Nativity of the Prophet).

The Beginning of the Hijri months (the first day of the month is indicated):

- Jumada al-ahira - 14th of January;
- Rajab - 13th of February;
- Sha'ban -14th of March;
- Ramadan - 13th of April;
- Shawwal - 13th of May;
- Zu-l-kada - 11th of June;
- Zu'l-hidjjah - 11th of July;
- Muharram - 9th of August;
- Safar - 8th of September;
- Rabiu-l-avval - 7th of October.