Question 1

What day of the week is a specific date?

Accepted Answer

You can find the day of the week for any date by using an online weekday calculator, which applies the Gregorian calendar algorithm to return the correct weekday instantly. For dates in the past, the calculation must account for leap years and calendar reforms to be accurate. Enter the full date — day, month, and year — and the tool returns the weekday name along with the ISO week number.

Question 2

How do I find the day of the week for a date in Excel?

Accepted Answer

In Excel, use the TEXT function to display the weekday name: =TEXT(A1, 'dddd') returns the full weekday name like 'Monday' for the date in cell A1. Alternatively, WEEKDAY(A1, 2) returns a number from 1 (Monday) to 7 (Sunday) using ISO numbering, which is useful for conditional logic and sorting. These functions work on any valid Excel date value.

Question 3

What is the Doomsday algorithm?

Accepted Answer

The Doomsday algorithm is a mental math method invented by mathematician John Conway to calculate the day of the week for any date in your head. It relies on the fact that certain easy-to-remember dates — called doomsdays — always fall on the same weekday within any given year. By finding the doomsday for a given year and then counting forward or backward, you can determine the weekday for any date in that year.

Question 4

What day of the week was I born on?

Accepted Answer

To find the weekday of your birth, enter your full birth date — including the year — into a weekday calculator, which will return the exact day of the week. Because the calendar pattern repeats roughly every 28 years for the same date-weekday combination, your birthday falls on the same weekday as your birth only occasionally. Many people find it a fun and meaningful piece of personal trivia to know.

Question 5

What is ISO weekday numbering?

Accepted Answer

The ISO 8601 standard assigns weekday numbers from 1 (Monday) to 7 (Sunday), making Monday the first day of the week. This differs from some regional conventions where Sunday is day 1 (as in the US-style WEEKDAY function in Excel with mode 1). ISO weekday numbering is widely used in international business, logistics, and programming to avoid regional ambiguity.

Question 6

Why do some calendars start the week on Monday and others on Sunday?

Accepted Answer

The choice of week start day is rooted in religious and cultural tradition: the Judeo-Christian Sabbath on Saturday led many Western cultures to treat Sunday as a day of rest and the start of a new week. However, the ISO 8601 international standard defines Monday as day 1 of the week because it is the first working day. Most of Europe, and international business generally, follows the Monday-start convention, while the US, Canada, and several other countries retain Sunday as the week's start.

Question 7

Can I find the day of the week for historical dates before the Gregorian calendar?

Accepted Answer

Calculating weekdays for dates before the Gregorian calendar reform of 1582 requires specifying whether you want the proleptic Gregorian calendar (extending the Gregorian rules backward) or the Julian calendar (which was in use at the time). The two calendars differ by days, so a weekday calculator must use the appropriate calendar system to give a historically accurate answer. Most online tools default to the proleptic Gregorian calendar unless you specify otherwise.

Question 8

How do I find the week number and quarter for a date?

Accepted Answer

The ISO week number for a date can be found using Excel's ISOWEEKNUM(date) function or any weekday calculator that displays week metadata. The quarter is determined by the month: Q1 is January–March, Q2 April–June, Q3 July–September, and Q4 October–December. These figures are frequently used in business reporting, fiscal planning, and project management to group dates into standard reporting periods.

date	weekday	note
2026-01-01	Thursday	New Year's Day 2026 falls on a Thursday
2026-08-15	Saturday	India Independence Day 2026 falls on a Saturday
2026-12-25	Friday	Christmas Day 2026 falls on a Friday — making a long holiday weekend
1969-07-20	Sunday	Apollo 11 Moon landing (July 20, 1969) was a Sunday
2000-01-01	Saturday	The turn of the millennium — January 1, 2000 was a Saturday

📆 Weekday Calculator — 🇱🇰 Sri Lanka

How to Use the Weekday Calculator in Sri Lanka

Real-World Examples for Sri Lanka

Frequently Asked Questions

What day of the week is a specific date?

How do I find the day of the week for a date in Excel?

What is the Doomsday algorithm?

What day of the week was I born on?

What is ISO weekday numbering?

Why do some calendars start the week on Monday and others on Sunday?

Can I find the day of the week for historical dates before the Gregorian calendar?

How do I find the week number and quarter for a date?

📆 Weekday Calculator — 🇱🇰 Sri Lanka

How to Use the Weekday Calculator in Sri Lanka

Real-World Examples for Sri Lanka

Frequently Asked Questions

What day of the week is a specific date?+

How do I find the day of the week for a date in Excel?+

What is the Doomsday algorithm?+

What day of the week was I born on?+

What is ISO weekday numbering?+

Why do some calendars start the week on Monday and others on Sunday?+

Can I find the day of the week for historical dates before the Gregorian calendar?+

How do I find the week number and quarter for a date?+

More Free Date & Time Tools

What day of the week is a specific date?

How do I find the day of the week for a date in Excel?

What is the Doomsday algorithm?

What day of the week was I born on?

What is ISO weekday numbering?

Why do some calendars start the week on Monday and others on Sunday?

Can I find the day of the week for historical dates before the Gregorian calendar?

How do I find the week number and quarter for a date?