Conway’s Doomsday algorithm

E163256

calendar algorithm day-of-week calculation method mental calculation method

Conway’s Doomsday algorithm is a mental calculation method devised by mathematician John Horton Conway for quickly determining the day of the week for any given date.

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All labels observed (3)

Label	Occurrences
Doomsday rule	5
Doomsday algorithm	2
Conway’s Doomsday algorithm canonical	1

How this entity was disambiguated

This entity first appeared as the object of triple T1428686 — resolving that mention is where its identity was fixed. The disambiguator weighed these candidate entities and picked the highlighted one (or “None”, minting a new entity). This is how homonymy is resolved: the same surface form can point to different entities.

NED1 Entity disambiguation (via context triple) gpt-5-mini-2025-08-07

Target entity: Conway’s Doomsday algorithm
Context triple: [John Horton Conway, notableWork, Conway’s Doomsday algorithm]

A. The Calendar
"The Calendar" is a crime thriller play by Edgar Wallace that blends mystery and melodrama around horse racing and high society intrigue.
B. When the Nines Roll Over
"When the Nines Roll Over" is a collection of contemporary short stories by David Benioff that explores themes of love, ambition, and disillusionment in modern urban life.
C. The Extra Day
The Extra Day is a 1956 British comedy film starring Sydney Chaplin, centered on the humorous misadventures that occur when a film production is unexpectedly delayed.
D. A Monday Date
"A Monday Date" is a classic jazz composition closely associated with pioneering American jazz pianist and bandleader Earl Hines.
E. Look-and-say sequence
The look-and-say sequence is a famous integer sequence where each term is generated by verbally describing the digits of the previous term, studied for its surprising combinatorial and growth properties.
F. None of above. chosen
G. Unsure - the case is ambiguous/there is not enough information to decide.

NED2 Entity disambiguation (via description) gpt-5-mini-2025-08-07

Target entity: Conway’s Doomsday algorithm
Target entity description: Conway’s Doomsday algorithm is a mental calculation method devised by mathematician John Horton Conway for quickly determining the day of the week for any given date.

A. The Calendar
"The Calendar" is a crime thriller play by Edgar Wallace that blends mystery and melodrama around horse racing and high society intrigue.
B. When the Nines Roll Over
"When the Nines Roll Over" is a collection of contemporary short stories by David Benioff that explores themes of love, ambition, and disillusionment in modern urban life.
C. The Extra Day
The Extra Day is a 1956 British comedy film starring Sydney Chaplin, centered on the humorous misadventures that occur when a film production is unexpectedly delayed.
D. A Monday Date
"A Monday Date" is a classic jazz composition closely associated with pioneering American jazz pianist and bandleader Earl Hines.
E. Look-and-say sequence
The look-and-say sequence is a famous integer sequence where each term is generated by verbally describing the digits of the previous term, studied for its surprising combinatorial and growth properties.
F. None of above. chosen

Statements (48)

Predicate	Object
instanceOf	calendar algorithm ⓘ day-of-week calculation method ⓘ mental calculation method ⓘ
advantage	avoids large multiplications ⓘ suitable for mental contests and demonstrations ⓘ
appliesTo	Gregorian calendar ⓘ linked to: Gregorian calendar (Western churches) Julian calendar ⓘ
basedOn	Doomsday rule ⓘ linked to: Conway’s Doomsday algorithm
characteristic	can be performed mentally without written notes ⓘ relies on memorized reference dates ⓘ uses simple integer arithmetic ⓘ
creator	John Horton Conway ⓘ linked to: John H. Conway
developedBy	John Horton Conway ⓘ linked to: John H. Conway
difficulty	requires memorization of anchor days and patterns ⓘ
field	calendar calculation ⓘ mental arithmetic ⓘ recreational mathematics ⓘ
goal	enable fast mental day-of-week computation ⓘ
hasComplexity	constant time with respect to date size ⓘ
hasReferenceDate	10/10 (10 October) ⓘ 11/7 (7 November) ⓘ 12/12 (12 December) ⓘ 14 March (non-leap years) ⓘ 29 February (leap years) ⓘ 4/4 (4 April) ⓘ 5/9 (9 May) ⓘ 6/6 (6 June) ⓘ 7/11 (11 July) ⓘ 8/8 (8 August) ⓘ 9/5 (5 September) ⓘ last day of February ⓘ
hasStep	adjust for leap years when necessary ⓘ compute year’s Doomsday from last two digits of year ⓘ find century anchor day ⓘ use memorized Doomsday dates within month ⓘ
namedAfter	Doomsday (reference weekday for a year) ⓘ linked to: Doomsday of a year
notableFor	speed of mental day-of-week calculation ⓘ
publicationContext	popularized in expository and recreational mathematics writings ⓘ
relatedTo	Tomohiko Sakamoto’s algorithm ⓘ Zeller’s congruence ⓘ perpetual calendar ⓘ
teachingUse	illustrate modular arithmetic in a practical context ⓘ
typicalInput	calendar date (day, month, year) ⓘ
typicalOutput	day of the week ⓘ
use	determine day of the week for a given date ⓘ
usesConcept	Doomsday of a year ⓘ anchor day ⓘ leap year ⓘ

How these facts were elicited

Referenced by (8)

Full triples — surface form annotated when it differs from this entity's canonical label.

John Horton Conway → notableWork → Conway’s Doomsday algorithm ⓘ

subject linked to: Horton

John H. Conway → notableWork → Doomsday algorithm ⓘ

subject linked to: John