Eid al-Fitr is celebrated at the end of the Islamic holy month of Ramadan and begins when the moon is sighted after sunset.
However, the end date always changes each year, as the timing is based on the lunar calendar.
This calendar is 11 days shorter than the Gregorian calendar.
The Saudi Supreme Court announced the start of Eid Al-Fitr will be Friday June 15, after reported sightings of the new moon, Saudi Press Agency reported.
Ramadan will therefore end tonight (Thursday, June 14) on the tenth month of the lunar calendar.
The Shawwal crescent was witnessed by many people and was easy to sight, according to Al-Ekhbariya.
Follow the latest updates here.
7pm update: What will you be doing tomorrow?
Eid al-Fitr is a public holiday in many Muslim countries, but is not a public holiday in the UK.
However, Muslims in the UK start the day by waking up early and gathering at the local mosque or an outdoor prayer ground for the Eid morning prayers.
Gifts and greeting cards are often exchanged and children may receive presents.
Biryani – a spicy meat and rice dish – is particularly popular in the UK on Eid.
Members of the Afghan community may enjoy bolani – a type of flatbread stuffed with spinach, potatoes, pumpkin or lentils.
6.53pm update: Celebrations begin
Many parts of the world are already marking the start of Ed al-Fitr.
Families and communities usually celebrate with massive feasts to mark the end of Ramadan, the holy month of fasting.
Over in Indonesia, a parade took place today in Yogyakarta.
Hundreds of children took to the streets in traditional clothing to celebrate Ramadan coming to a close.
6.44pm update: How do Muslins in the UK celebrate Eid?
Muslim communities organise events with various family activities in many UK cities, such as London and Birmingham,
The Birmingham gathering is the largest Eid celebration in Europe and last year more than 100,000 Muslims descended on Small Health Park.
On Eid al-Fitr there is a strong focus on charity and Muslims are expected to donate food or money to the poor.
The purpose of Eid is to thank Allah for the strength he provided to Muslims during the holy month of Ramadan.
6.35pm update: When will the UK celebrate?
There is a great deal of confusion over how the date of Eid al-Fitr is decided, as religious authorities in each nation have the right to declare the date according to the sighting of the new moon in their region.
Eid dates can differ around the world, but this is usually within one or two days of each other.
The date of Eid al-Fitr is determined on the sighting of the crescent moon following the new moon.
A new moon was observed in the UK on June 13, and a crescent moon is expected tonight, June 14.