Ever wondered what day of the week a historical event fell on, or what weekday your next vacation lands? Our free day of the week calculator instantly determines the day (Sunday to Saturday) for any Gregorian date from 1582 onward, including leap years and future predictions. Ideal for genealogy buffs tracing birthdays, planners scheduling events, or trivia lovers, this weekday calculator uses precise algorithms—no calendars required. Enter a date and discover!
Calendars shift with leap years and reforms, but our tool handles it all seamlessly. Learn how to use it here.
What is a Day of the Week Calculator?
A day of the week calculator applies mathematical formulas (like Zeller’s Congruence) to compute weekdays based on year, month, and day, accounting for calendar changes like the Gregorian switch in 1582.
Essential for:
- Historical research (e.g., “What day was July 4, 1776?”).
- Personal milestones (birthdays, anniversaries).
- Future planning (weddings, holidays up to 3000).
Ours adds extras like zodiac signs, holidays, and monthly calendars for context.
Features of Our Free Weekday Calculator
Built for accuracy and fun, this calculate day of the week tool provides:
- Wide Date Range: 1582–3000 AD, Gregorian/Julian toggle.
- Instant Results: Day name, plus facts (e.g., “Black Friday”).
- Step-by-Step Breakdown: Optional Zeller’s formula workings.
- Visual Calendar: See the full month view.
- Mobile-Optimized: Quick access anywhere, unlimited use.
Stands out with trivia integration, unlike plain calculators.
How to Use the Day of the Week Calculator
- Enter Date: Select year, month, day (e.g., 1969-07-20 for Moon landing).
- Choose Calendar: Gregorian (default) or Julian for pre-1582.
- Calculate: Get the weekday, zodiac, and facts.
- View More: Expand for formula steps or calendar.
Tip: For batch checks, use the monthly view to scan weekdays at a glance.
Zeller’s Congruence: How to Calculate Day of the Week Manually
Zeller’s Congruence (h = (q + floor((13(m+1))/5) + K + floor(K/4) + floor(J/4) – 2J) mod 7) determines the day, where:
- h=0=Saturday, 1=Sunday, …, 6=Friday
- q=day of month
- m=month (3=March, 1=Jan/Feb of next year)
- K=year of century (year mod 100)
- J=century (floor(year/100))
Example: For July 20, 1969 (Moon landing):
m=7, q=20, year=1969 → K=69, J=19. h = (20 + floor(13*8/5) + 69 + floor(69/4) + floor(19/4) – 2*19) mod 7 = 3 → Sunday.
Day of the Week Examples: Historical & Future Dates
Test with these:
Historical: Independence Day
July 4, 1776: Thursday—sparking weekend debates on celebrations.
Personal: Your Birthday
Input your birthdate for the weekday and fun facts (e.g., born on a Tuesday? “Tuesday’s child is full of grace”).
Future: New Year’s 2030
January 1, 2030: Wednesday—perfect for mid-week resolutions.
| Date | Event | Weekday | Fun Fact |
|---|---|---|---|
| July 4, 1776 | US Independence | Thursday | John Adams wanted July 2; fireworks on 4th. |
| July 20, 1969 | Moon Landing | Sunday | “One small step” aired during prime time. |
| December 25, 2025 | Christmas | Thursday | Long weekend for many with Dec 26 off. |
| January 1, 2100 | New Year | Saturday | Not a leap year; weekend start. |
FAQ: Common Day of the Week Calculator Questions
- How does leap year affect day calculations?
- February 29 shifts subsequent days; our tool auto-adjusts.
- Can I calculate for dates before 1582?
- Yes, via Julian mode for pre-Gregorian accuracy.
- What’s the formula behind it?
- Zeller’s Congruence—detailed steps available on request.
Unlock date mysteries—try our free day of the week calculator and plan smarter. Share your surprising finds below!