Day of Week Calculator

Overview

How to use this calculator

1. Enter the calendar year of the date you are interested in, such as 1990, 2025, or 2050.
2. Enter the month as a number from 1 (January) through 12 (December).
3. Enter the day of the month, making sure it falls within the valid range for that month and year (for example, February 29 is valid only in leap years).
4. Run the calculation to see the weekday index, weekday name, and a weekend flag that shows whether the date falls on Saturday or Sunday.
5. Use the weekday name to schedule meetings, appointments, or travel, or to verify the day for birthdays, anniversaries, and historical events.
6. If you are coordinating across time zones, decide which local calendar you are anchoring to (for example, the event location’s time zone) and use that as your reference date.

Inputs explained

Year

The four-digit year for the date you are checking, such as 1985, 2024, or 2030. The calculator assumes the proleptic Gregorian calendar, which aligns with the modern calendar for most practical dates.

Month

The month number from 1 through 12. For example, 1 = January, 2 = February, 3 = March, up to 12 = December. Be sure to match the month with a valid day and year combination (for instance, use 2/29 only in leap years).

Day

The day of the month for the date you want to check. Valid ranges differ by month (for example, 30 days in November, 31 in July). The calculator expects a valid date; an invalid combination may produce an unexpected result depending on the underlying date engine.

Outputs explained

Day index (0=Sun)

A numeric weekday index following the JavaScript `getDay()` convention: 0 = Sunday, 1 = Monday, 2 = Tuesday, 3 = Wednesday, 4 = Thursday, 5 = Friday, 6 = Saturday. This is useful when building automations or integrating with code that expects numeric weekdays.

Day name

The plain-language weekday name corresponding to the index, such as Monday, Wednesday, or Saturday. This is the most human-friendly representation for most uses.

Weekend? (1=yes)

A simple flag that marks Saturdays and Sundays as weekend days (1) and Monday through Friday as weekdays (0). This reflects common North American and European workweek patterns; some regions use different weekend days.

When to use it

• Checking whether a project deadline, exam date, or launch date falls on a weekday or a weekend.
• Verifying the day of the week for birthdays, anniversaries, historical events, or holiday observances.
• Planning recurring meetings by testing which calendar dates land on a specific weekday in a given month or year.
• Coordinating travel and time off by seeing whether your departure or return falls on a workday.
• Building simple tools or scripts that need to convert dates into weekdays without re-implementing date math.

Tips & cautions

• If you are planning events that span time zones, pick the location whose calendar matters most—for example, the local time at the event site—and enter that date here to determine the weekday.
• Pair this calculator with a date-add or date-difference tool to see how shifting a deadline by a certain number of days changes the weekday.
• Remember that some countries and organizations treat Friday or other days as part of the weekend; use the day name to reason about those custom definitions.
• For historical research, confirm that the date you are using is in the Gregorian calendar; older dates in some regions may have used the Julian calendar with different weekday alignments.
• The weekend flag is based on a Saturday/Sunday weekend convention and does not adapt to regions with Friday–Saturday or other nonstandard weekends.
• The calculator assumes the Gregorian calendar for all dates; it does not model historical calendar reforms or switches between Julian and Gregorian calendars in specific countries.
• It does not account for holidays or local non-working days—only the raw weekday is shown.
• Extremely old or far-future dates may behave differently depending on how the underlying date engine handles them, and small inconsistencies may appear compared to specialized historical calendar tools.

Worked examples

Deep dive

FAQs

Can this calculator handle historical dates far in the past?

For most practical purposes, yes. It applies the Gregorian calendar rules to all dates, which matches the modern calendar for recent centuries. However, some countries adopted the Gregorian calendar at different times, so for very old dates official historical weekdays may differ from this simplified model.

What if my weekend is Friday and Saturday instead of Saturday and Sunday?

The built-in weekend flag assumes Saturday and Sunday as the weekend. If your workweek is different, use the weekday name or index and apply your own logic—for example, treat index 5 (Friday) and 6 (Saturday) as weekend days.

Does daylight saving time or time zone changes affect the weekday result?

No. The weekday is tied to the calendar date, not the clock time. Daylight saving time changes may shift the local time but do not alter which weekday a date belongs to in this simplified approach.

Can I use this to schedule recurring events such as "every second Tuesday"?

Yes. You can plug in candidate dates and check which weekday they fall on, then build a list of dates that match your pattern. For complex recurrence rules, you may still want a dedicated calendar tool, but this calculator gives you a quick way to verify individual dates.

Why does the index start at 0 for Sunday?

The index follows the JavaScript `getDay()` convention where Sunday is 0 and Saturday is 6. Many programming environments use the same mapping, which makes it convenient for anyone who needs both human-readable names and numeric weekdays for scripts or integrations.

Related calculators