Quick answer
The day of the year counts days since 1 January, plus one. 1 March 2024 is day 61 because 2024 is a leap year (31 + 29 + 1), and it falls on a Friday.
Enter a date. The calculator returns the day number and the weekday.
Related tools: Day of the Week Calculator: Find the weekday of any date. Leap Year Calculator: Check whether a year is a leap year. Week Number Calculator: ISO 8601 week number of a date.
How to use the Day of the Year Calculator
- Pick date.
- Press Calculate to see the result, and use Reset to start again.
| Input | What to enter | Allowed values |
|---|---|---|
| Date | A calendar date | — |
Formula and method
Formula
day of year = days since 1 January + 1
Exact integer day arithmetic in UTC; no daylight-saving or time-zone effects.
Counts days within the date's year; leap years have 366.
Worked examples
These examples are verified: each one is an automated test case that the live calculator must reproduce exactly.
Example 1
Inputs: Date = 2024-03-01.
| Result | Value |
|---|---|
| Day of the week | Friday |
| Day of the year | 61 |
Example 2
Inputs: Date = 2023-12-31.
| Result | Value |
|---|---|
| Day of the week | Sunday |
| Day of the year | 365 |
The first line is the headline result (day of the week). Below it the day of the Year Calculator lists day of the year, which describe the same case from other angles. Exact integer day arithmetic in UTC; no daylight-saving or time-zone effects.
Leap years
In a non-leap year 1 March is day 60; in a leap year it is day 61. Leap years add 29 February, so every date after it shifts by one. The last day of the year is 365 or 366.
Where it is used
Ordinal dates (YYYY-DDD) appear in logistics, astronomy and data logs, and gardeners track the days since the last frost. ISO 8601 allows the ordinal format.
Ordinal dates and leap years
The day of the year counts from 1 January as day 1. In the leap year 2024, 1 March is day 61 (31 + 29 + 1); in a common year it is day 60. A year has 365 days, or 366 in a leap year, so 31 December is day 365 or 366.
ISO 8601 calls this the ordinal date and writes it as year-day, for example 2024-061. It is used in logistics, astronomy and manufacturing date codes.
Day of the Year from different start dates
The same calculator run from 1 January of four consecutive years.
| Date | Day of the week | Day of the year |
|---|---|---|
| 2026-01-01 | Thursday | 1 |
| 2027-01-01 | Friday | 1 |
| 2028-01-01 | Saturday | 1 |
| 2029-01-01 | Monday | 1 |
What happens with invalid input
These messages are produced by the calculator itself, so you know what to fix.
- Date: left empty shows "Enter date." beside that field and no result.
Choosing between the Day of the Year Calculator and similar calculators
Each row shows what a related calculator on this site asks for and what it returns, so you can pick the one that matches your question.
| Calculator | You enter | It returns |
|---|---|---|
| [Day of the Week Calculator](/date-calendar/day-of-the-week-calculator/) | date | Day of the week |
| [Leap Year Calculator](/date-calendar/leap-year-calculator/) | year | Result |
| [Week Number Calculator](/date-calendar/week-number-calculator/) | date | ISO week number |
| [Birth Year Calculator](/date-calendar/birth-year/) | age | Birth year |
| [Graduation Year Calculator](/date-calendar/graduation-year/) | start year and program length | Graduation year |
Background: dates and times
Date and time results depend on the conventions a tool uses: whether the end date counts, whether weekends and holidays are skipped, how months of different lengths are handled and whether time zones are applied. This page states its convention, and the worked examples show it.
Dates use the Gregorian calendar and calendar days unless the page says otherwise; check deadlines against the rule in your contract or regulation.
Assumptions and limitations
- Leap years
If a required value is empty, not a number, or outside its allowed range, the form marks that field with a message and shows no result instead of a misleading number. The automated checks deliberately try invalid entries for date to confirm this.
Frequently asked questions
What day of the year is 31 December?
365, or 366 in a leap year.
Is today day 100?
Enter today's date to see.
Is the Julian day the same?
No, a Julian day number counts continuously.
What is the day number of 31 December?
365 in a common year and 366 in a leap year.
Why is 1 March day 61 in 2024?
2024 is a leap year, so January (31) and February (29) give 60 days before 1 March, making it day 61.
What does the Day of the Year Calculator calculate?
Which day of the year a date falls on. It returns Day of the week and Day of the year.
What formula does the Day of the Year Calculator use?
day of year = days since 1 January + 1. Counts days within the date's year; leap years have 366.
What do I need to enter in the day of the Year Calculator?
You enter Date.
How is the result rounded or limited?
Exact integer day arithmetic in UTC; no daylight-saving or time-zone effects. Leap years.
What is an example of a day of the Year result?
With date 2024-03-01, the day of the week is Friday.
Where does the method come from?
The method follows: ISO 8601-1: Date and time, representations for information interchange (calendar dates, ordinal dates and week dates): ordinal date, day 1 to 365 or 366; Gregorian calendar reform, papal bull Inter gravissimas (1582): the leap-year rule.
Related calculators
- Day of the Week Calculator — Find the weekday of any date.
- Leap Year Calculator — Check whether a year is a leap year.
- Week Number Calculator — ISO 8601 week number of a date.
- Birth Year Calculator — Year of birth from a person's age.
- Graduation Year Calculator — Expected graduation year from the start year and program length.
- New Year's Countdown — Countdown to New Year's Day: the days remaining until 1 January from any date.
- Academic Year Difference Calculator — Number of academic years between two academic years such as 2019–20 and 2023–24.
Sources
- ISO 8601-1: Date and time, representations for information interchange (calendar dates, ordinal dates and week dates): ordinal date, day 1 to 365 or 366
- Gregorian calendar reform, papal bull Inter gravissimas (1582): the leap-year rule
Content last reviewed 2026-11-04. Formulas and worked examples are checked by automated tests against independently computed values.