When Is Halloween?

Halloween is October 31.

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What day of the week is Halloween?

October 31 never moves, so the only thing that changes is the weekday. And for Halloween, unlike almost any other holiday, the weekday is the whole ballgame: a Saturday Halloween means parties and a full evening of trick-or-treating, while a Tuesday Halloween means everyone celebrates on the weekend before and the actual night is a school night.

The rule is simple. Halloween advances one weekday each year, because a 365-day year is 52 weeks plus a day, and two after a leap year. A Saturday Halloween only comes around every five or six years, which is why some years feel like a much bigger deal than others.

Year	Halloween falls on	Shift

Need the weekday for a year outside this range, or any other date? Our day-of-the-week calculator covers any date from 1900 onward.

Why is Halloween on October 31?

Because it is the eve of All Saints' Day. That is the entire answer, and it is hiding in the name: All Saints' Day was also called All Hallows, so the night before was All Hallows' Eve, which wore down over centuries into Hallowe'en and then Halloween. The apostrophe in the older spelling is standing in for the missing "v" in "even".

So the real question is why All Saints' Day is on November 1. In the eighth century Pope Gregory III dedicated an oratory in St Peter's Basilica in honour of all the saints on November 1. A century later Pope Gregory IV asked Louis the Pious to proclaim it across the Holy Roman Empire. November 2 was added later as All Souls' Day, around the year 1000. Halloween is the front end of a three-day sequence about the dead.

Where does Samhain fit in?

Samhain was a Gaelic festival marking the end of the harvest and the beginning of the darker half of the year, observed around the same point in the calendar. Many Halloween customs are commonly traced to it, and the overlap in timing is real.

Two cautions, because this is territory where confident claims outrun the evidence.

Samhain was not a god. You will see it stated that Samhain was "the Celtic lord of the dead". This is a persistent error that has been repeated by otherwise reputable sources. Samhain is the name of the festival, from an Old Irish word meaning roughly "summer's end".
How much Halloween descends from Samhain is genuinely debated. The tidy story that the church deliberately dropped All Saints' Day on top of a pagan festival to absorb it is a claim, not a settled fact. Gregory III's November 1 dedication was in Rome, which was not exactly Celtic territory. The customs we now recognise as Halloween took their modern shape much later, largely in Ireland and Scotland, and arrived in America with nineteenth-century immigrants.

The honest summary: October 31 is Christian in its naming and its date, and a good deal of the folk practice around it has Gaelic roots. Anyone telling you it is purely one or purely the other is selling something.