When Ramadan officially ends, the daily fasting is over and the next month - Shawwal - starts with the festivities of Eid al-Fitr.
The dates aren't known until a day or two beforehand because the Islamic calendar is based on the lunar cycle.
If the first crescent of the new moon is seen at Mecca before sunset on the 29th day, then that month is deemed to have ended and the next month begins.
If the moon isn't seen - for reasons such as heavy cloud cover - then the month carries on for one more day and the next month starts the day after that.
Because Islam follows a lunar calendar, dates drift back by 11 days a year in the sun-based Gregorian calendar used by most of the rest of the Western world.
In some parts of the world, Muslim officials instead use astronomical charts to follow the cycle of the moon, rather than relying on observation.
It allows governments in some Muslim-majority countries to plan public holidays and civic events in advance rather than wait for a moon sighting at the last minute.
It also means the dates of Ramadan and Eid are already mapped out.
And for those that do still rely on sightings, it gives a very good idea of when Ramadan and Eid are likely to be, subject to a difference of a day or so.
For instance, the astronomical charts for 2017 said Eid al-Fitr would be on Sunday, June 25.
As with the dates for all Islamic months, the moon has to be seen at Mecca on the 29th day for the month to end that day. If it's not seen, the month goes on another day.
So, depending on whether the moon was seen on June 24, Eid was going to be on June 25 or June 26. And when the moon was sighted, it ended up taking place on June 25.
So what are the predicted dates of these events for 2018?
Here's all the info you need:
The first day of the month of fasting will be Wednesday, May 16, 2018, based on astronomical charts, and subject to a moon sighting close to that time. Ramadan is the ninth month of the Islamic calendar.
The earlier date means that Ramadan is se to be finished before the longest day of the year. But it still falls within the long, warm days of summer so there will be extended periods of daily fasting, lasting almost 19 hours.
As the months move back through the Western calendar, Ramadan is set to begin in April by 2020, in March by 2023 and in February by 2026. That means the daily hours of fasting will get shorter, offering some comfort to those who struggle to go without food and drink for such long periods.
Eid al-Fitr 2018
The Eid festivities of the first day of the new month of Shawwal will be on Friday, June 15, 2018, based on astronomical charts, and subject to a moon sighting close to that time.
As with Ramadan, Eid will get earlier and earlier as the years go on, meaning the weather for Birmingham's outdoor Eid celebrations in Small Heath Park might be colder and wetter. Prayers are moved to local mosques if conditions are too miserable.
Eid al-Adha 2018
The second set of annual Eid festivities - translating as the Feast of the Sacrifice - starts on the 10th day of the month of Dhu al-Hijjah (the 12th and final month of the Islamic calendar) and lasts until the 13th day.
The 10th day falls on Tuesday, August 21, 2018, according to astronomical charts and subject to a moon sighting close to that time.
This event still involves outdoor prayers in Birmingham's Small Heath Park. As with Eid ul Fitr, the prayers would be moved indoors to local mosques if the weather is bad.
So you can now pencil in those dates in your diaries and on your calendars and have some idea when next year's Ramadan fasting and Eid festivities will happen.