DocomintBuscador del Día de la Semana
Encuentra en qué día de la semana cae (o caerá) cualquier fecha, además de su día del año y trimestre.
What is a Buscador del Día de la Semana?
Finds the weekday for any date — a birthday, a historical event, a future appointment — instantly rather than counting weeks on a mental calendar, plus three related figures (day of year, ISO week number, and calendar quarter) that come up in scheduling and reporting contexts.
How to use the Buscador del Día de la Semana
- Enter any date, past or future
- Press Find Day
- The weekday, day-of-year number, ISO week, and quarter all appear instantly, computed on your device
Formula
Uses the Gregorian calendar's standard date-to-weekday calculation
Alongside the weekday, it also reports day-of-year, ISO week number, and calendar quarter for the same date.
Example
August 8, 2026 falls on a Saturday — the 220th day of the year, in ISO week 32, within Q3.
Common mistakes
- Assuming this switches to the Julian calendar for dates before 1582, when the Gregorian calendar wasn't yet adopted everywhere — it uses the proleptic Gregorian calendar consistently for all dates.
- Confusing the ISO week number shown with a simple "week of the month" count — they're different systems entirely.
- Assuming "day of year" starts at 0 for January 1st — it starts at 1.
Frequently asked questions
How far back or forward in time does this work?
It works for any date the browser's Date object can represent — effectively many thousands of years in either direction — though results for dates before widespread adoption of the Gregorian calendar (pre-1582 in most of Europe) won't match historical calendars actually in use at the time.
What calendar system does this use?
The Gregorian calendar — the internationally standard calendar used by virtually all modern software, and the one in civil use across most of the world today.
Does this account for the switch from the Julian to Gregorian calendar?
No — it applies the modern Gregorian calendar consistently to every date, including historical ones. Dates before the Gregorian calendar's actual adoption (which happened at different times in different countries, mostly around 1582 onward) won't match the calendar that was really in civil use at the time.
What's the difference between day-of-year and ISO week number?
Day-of-year is a simple sequential count (1 to 365 or 366). ISO week number groups dates into Monday-Sunday weeks per the ISO 8601 standard, where week 1 is defined as the week containing the year's first Thursday — a more specific rule than dividing day-of-year by 7.
Is my numbers uploaded anywhere?
No — Buscador del Día de la Semana runs entirely in your browser using JavaScript/WebAssembly. Your numbers is never sent to a server.