Eleven days a year: planning travel against a moving calendar.

The drift, and why it governs everything

The Hijri year is twelve lunar months and runs to about three hundred and fifty four days, roughly eleven days shorter than the Gregorian year. Every Islamic observance therefore arrives about eleven days earlier each year against the Western calendar, and works its way backwards through all four seasons over a cycle of roughly thirty three years. After sixteen or seventeen years an observance sits in the opposite season from where it sits today; after thirty three it has come home.

For a family that travels to the same country repeatedly, that is not an abstraction. It decides the weather you will meet, whether the trip collides with school terms, whether Eid falls inside a Thai high season or outside it, what a hotel room costs, and whether the Andaman coast is dry or under rain. Two identical itineraries eight years apart are not the same trip at all. The families who plan well treat the calendar as the first variable rather than the last.

Where the year sits at present

As this is written, the pattern runs as set out below. Every one of these positions moves earlier by about eleven days each year, and every date depends on the sighting of the moon and on the announcement made by your own authority, so treat this as a map of relationships and not as a timetable. Confirm your own dates locally before you commit to anything.

Read down the last column and the planning consequences appear on their own. Ramadan currently coincides with Thailand's most comfortable weather, which is why a Ramadan stay here is easier now than it will be in a decade. Eid al-Adha currently lands in the heat. And the observances of Muharram and Rabi al-Awwal currently fall inside the Gulf summer, which is the season that matters most to this desk, because it is when families come for months rather than days.

The collision that matters: the Gulf summer

The single largest fixture in our year is the Gulf summer. From June to August, when home temperatures reach the high forties, families travel and stay for weeks or months, often with children out of school and often with three generations in the party. That season is fixed to the Gregorian calendar, because it is driven by the sun and by school terms. The Hijri observances are not fixed, and they slide through it.

At present, Islamic New Year, Ashura and Mawlid all fall inside or at the edges of that window, which means a long summer stay in Thailand will contain at least one observance. In about eight years Ramadan itself will begin to touch the early part of it, and roughly sixteen years from now the whole month will sit in the Gulf summer, which will change the shape of these stays completely: a fasting family in Thailand in July, in the green season, is a different operation from a fasting family in Bangkok in February. We plan on that horizon because some of our clients own property here and think in decades.

Booking against a date nobody knows yet

The practical difficulty is not the drift, which is predictable, but the last day of uncertainty. The start of Ramadan and the days of both Eids depend on the sighting of the moon and are confirmed only a day or so in advance, and different countries announce differently. Public holidays across the Gulf states are likewise declared close to the event. A family cannot know in January exactly which evening Eid dinner will fall on, but it must book the room in January if it wants one.

• Hold two consecutive dates for anything that has to happen on the day itself
• Negotiate the cancellation window at the time of booking, in writing, not later
• Book flights on flexible fares for the Eid legs, and fixed fares for the rest
• Reserve villas and large suites early, since the Eid weeks sit inside Thai high season
• Ask the hotel to hold the second night without charge, which good properties will do
• Keep one office holding every booking, so a one day shift moves everything at once
• Confirm the actual dates with your own authority as soon as they are announced

School terms, work calendars and the rest of the year

Two more calendars sit on top of the Hijri one and both matter. Gulf school terms follow the Gregorian year and their long break is the summer, which is why the summer exodus is fixed while the observances move. Where children are at school in Thailand on a longer stay, the Thai and international school calendars follow their own pattern again, with the main break in the Thai hot season around April and shorter breaks around the new year. Families with children in both systems, which is more common than you might think, plan around the intersection of three calendars.

Thailand's own public holidays are worth marking as well, since they close government offices and fill hotels. Songkran in April, the Thai new year, is the busiest domestic travel week of the year and the hardest week to move around the country. The new year period at the end of December is the peak of the international season on both coasts. Neither is connected to the Hijri calendar, and both will collide with one Islamic observance or another as the years turn. Our living in Thailand guides set out the Thai calendar in full.

How we plan it

For families we look after year after year we keep a rolling five year view: the approximate Hijri positions, the Gulf summer window, school terms on both sides, and the Thai seasons laid over the top. It is not precise, because it cannot be, but it is accurate enough to answer the questions that actually get asked, which are whether next year's Eid will be hot, whether the year after is a good one for a long Ramadan stay in Phuket, and when to buy or renew a lease so that the family's usual months are covered.

The discipline is to plan structure early and dates late. Decide the shape of the year in advance, hold options generously, and confirm the exact days when the announcement is made. That is how the households we serve manage to keep a month that moves inside a life that does not, and it is a good deal less complicated in practice than it sounds on paper.

Every date above is approximate and moves: all Islamic observances depend on the sighting of the moon and are announced locally, so the day declared in Thailand can differ from the day declared in your own country. Confirm your dates with your own mosque or Islamic authority at home, and with the Office of the Chularatchamontri and the Central Islamic Council of Thailand (halal.or.th) for the Thai announcement. Confirm Thai public holidays with the Tourism Authority of Thailand or a Thai government source, and entry requirements with the Royal Thai Embassy in your country.

This briefing is general information, not legal, tax or investment advice. Thai rules change frequently and individual cases differ. Verify current requirements with the relevant authorities, including the Immigration Bureau, the Board of Investment, the Land Department, the Department of Business Development and the Revenue Department, and take advice on your own facts before acting.