Day of the Week Calculator

The Day of the Week Calculator instantly determines what day of the week any date falls on. Whether you're curious about historical events, planning future occasions, or just want to know what day your birthday was, this tool provides accurate results for any date.

How It Works

Our calculator uses the Gregorian calendar system, which is the most widely used civil calendar worldwide. The calculation takes into account leap years, month lengths, and calendar adjustments to provide accurate day-of-week information.

The Zeller's Congruence Formula

The mathematical foundation for calculating days of the week is Zeller's Congruence:

h = (q + ⌊13(m+1)/5⌋ + K + ⌊K/4⌋ + ⌊J/4⌋ + 5J) mod 7

Where:

• h = day of week (0=Saturday, 1=Sunday, etc.)
• q = day of month
• m = month (3=March, 4=April, ... 14=February)
• K = year of century
• J = century

How to Use This Calculator

1. Enter Your Date: Input the date you want to check
2. View the Day: Instantly see which day of the week it falls on
3. Explore Details: Get additional information like day number, week number, and more

Common Use Cases

Birthday Lookups

Discover what day of the week you were born on! Many cultures believe the day you were born influences personality traits:

• Monday's child is fair of face
• Tuesday's child is full of grace
• Wednesday's child is full of woe
• Thursday's child has far to go
• Friday's child is loving and giving
• Saturday's child works hard for a living
• Sunday's child is bonny and blithe

Historical Events

Find out what day significant historical events occurred:

• Moon Landing (July 20, 1969) - Sunday
• D-Day (June 6, 1944) - Tuesday
• Declaration of Independence (July 4, 1776) - Thursday

Future Planning

Plan vacations, weddings, and events by knowing what day future dates fall on.

Understanding Calendar Systems

The Gregorian Calendar

Adopted in 1582, the Gregorian calendar corrected drift in the Julian calendar. Key features:

• Regular years have 365 days
• Leap years add February 29th
• Leap year rules: divisible by 4, except centuries unless divisible by 400

Leap Year Impact

Leap years affect day calculations:

• 2024, 2028, 2032 are leap years
• 1900 was NOT a leap year (century rule)
• 2000 WAS a leap year (divisible by 400)

Frequently Asked Questions

How far back can I calculate?

The calculator works for dates after the Gregorian calendar adoption (October 15, 1582). For earlier dates, results use the proleptic Gregorian calendar.

Why do weeks start on different days?

Different cultures have different week start conventions:

• Sunday-first: USA, Canada, Japan
• Monday-first: Most of Europe, Australia, ISO standard
• Saturday-first: Some Middle Eastern countries

What is ISO week numbering?

ISO 8601 defines week 1 as the week containing the first Thursday of the year. A year can have 52 or 53 weeks.

Can I calculate dates before 1582?

Yes, but note that the Gregorian calendar wasn't in use then. Results show what the day would be if the Gregorian calendar had been used.

Fun Day Facts

Named After Ancient Gods

• Sunday: Sun's day
• Monday: Moon's day
• Tuesday: Tiw's day (Norse god of war)
• Wednesday: Woden's day (Odin)
• Thursday: Thor's day
• Friday: Frigg's day (goddess of love)
• Saturday: Saturn's day

Note: This calculator provides accurate results for the Gregorian calendar system. For historical dates before October 1582 in some countries, the Julian calendar was in use and dates may differ.