Quickly find the weekday for any date with our fast, accurate Day of the Week Calculator. Whether you are planning events, researching historical dates, or optimizing posting schedules, this tool gives you the weekday, ISO day number, week number, and more in seconds.
What the Day of the Week Calculator does
Enter any calendar date, select a time zone, and get an instant breakdown of its weekday and related calendar metrics. The calculator decodes your date to tell you the full weekday name (like Monday or Friday), the ISO weekday number (1 for Monday through 7 for Sunday), and the ISO-8601 week number. It also provides helpful context such as the day of the year and how many days are in that month. This is invaluable for teams scheduling content across regions, travelers planning itineraries, and anyone managing time-sensitive tasks.
How to use the calculator
- Select a date using the date picker.
- Choose your preferred time zone for consistent interpretation.
- Click “Calculate Day of the Week.”
Because the input is a calendar date (without a clock time), the weekday typically remains consistent across time zones. However, choosing a time zone ensures that any derived values adhere to your regional standards and avoids ambiguity in cross-border contexts.
Why knowing the weekday matters
- Event planning: Avoid weekend or holiday clashes by confirming the weekday ahead of time.
- Publishing: Align blog posts, emails, and social media releases to high-engagement days.
- Workflows: Coordinate sprints, releases, and meetings around weekdays with fewer conflicts.
- History and genealogy: Verify the weekday of historical events or anniversaries.
Key outputs you will get
- Weekday name (e.g., Monday)
- ISO day number (Monday = 1 to Sunday = 7)
- ISO week number
- Day of the year and days in the month
- Leap year status
- Weekend indicator (Yes/No)
Accuracy and methods
Behind the scenes, modern date-time libraries rely on the proleptic Gregorian calendar for historical consistency and robust international time zone databases. This ensures your results remain accurate across years, including leap years, without you needing to remember complex rules such as those used by Zeller’s congruence or other manual algorithms. The calculator also uses ISO-8601 standards for weekday numbering and week calculation, which is widely adopted in business and analytics.
Tips for better scheduling
- Verify week numbers when coordinating with international teams; some markets rely heavily on ISO week conventions.
- Check whether a date falls on a weekend before committing to launches or events.
- Consider regional holidays in addition to the weekday for real-world planning.
Use cases and examples
Suppose you are planning a product announcement for a global audience. First, use the Day of the Week Calculator to confirm that your target date is a midweek day when engagement is typically higher. Next, note the ISO week number for consistent reference in project documentation. Finally, coordinate across time zones knowing your date is interpreted consistently, avoiding unnecessary confusion.
Get started
Enter any date, select a time zone, and let the Day of the Week Calculator do the rest. It’s quick, reliable, and built to support planners, marketers, analysts, and anyone who needs a trustworthy way to translate dates into actionable weekday insights.