Ready to calculate
Pick a date or enter a year + day number// find the day-of-year number for any date
Find the day-of-year number for any date instantly. Calculate which day number a date falls on, days remaining in the year, and week number. Free browser-based tool.
Ready to calculate
Pick a date or enter a year + day numberUse the date picker to select any date from the calendar.
Type a year and day number to reverse-lookup the calendar date.
Get day number, days remaining, week number, and year progress instantly.
The Day of Year Calculator tells you which numbered day any date falls on — from Day 1 (January 1) to Day 365 or 366 (December 31 on a leap year). It also supports reverse lookup: enter a year and a day number to get the calendar date.
The day-of-year number (also called ordinal date) is a sequential count starting from 1 on January 1st. For example, February 1st is Day 32, and December 31st is Day 365 (or Day 366 in a leap year).
Leap years have 366 days instead of 365. Any date after February 28th in a leap year will have a day number that is 1 higher than the same date in a non-leap year. This tool automatically detects leap years.
Instead of finding the day number for a date, reverse lookup lets you enter a year and a day number (e.g., Year 2025, Day 200) to find out which calendar date that corresponds to.
The ISO 8601 week number is a standardized way to count weeks. Week 1 is the week containing the first Thursday of the year. Weeks run Monday to Sunday. Some years have 53 weeks.
No. The Julian Day Number (JDN) is an astronomical count starting from January 1, 4713 BC. The day-of-year ordinal date this tool calculates resets to 1 every January 1st and is simpler for everyday use.
Yes. This tool supports any valid year. Simply type the year manually in the reverse lookup field, or use the date picker which supports a broad range of dates.
A day of year calculator converts any calendar date into its ordinal position within that year — a single number between 1 and 366 that tells you exactly how far through the year a particular date falls. January 1st is always Day 1, and December 31st is Day 365 (or Day 366 in a leap year). This numbering system is also called an ordinal date.
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Ordinal dates show up in more places than you might expect. Here are some common scenarios where knowing the day-of-year number is genuinely useful:
2025-200.log) for efficient sequential sorting and storage.You can calculate the ordinal day number manually with a little arithmetic. Start with the cumulative days for each month before your target month, then add the day of the month:
For example, March 15th in a non-leap year: 59 (days before March) + 15 = Day 74. In a leap year: 60 + 15 = Day 75. This tool handles all the arithmetic automatically, including leap year detection.
A leap year occurs when a year is divisible by 4, except for century years (divisible by 100), which must also be divisible by 400. So 2000 was a leap year, but 1900 was not. Leap years matter for day-of-year calculations because every date from March 1st onwards has a day number that is one higher in a leap year compared to a regular year.
The ISO 8601 standard defines a week numbering system where Week 1 is the week that contains the first Thursday of the year (equivalently, the week containing January 4th). Weeks run from Monday to Sunday. This means January 1st might actually fall in Week 52 or 53 of the previous year if it falls on a Friday, Saturday, or Sunday. Most years have 52 ISO weeks, but some have 53.
This tool also supports the reverse operation: if you know a year and an ordinal day number, you can find the corresponding calendar date. This is useful when working with systems or datasets that store dates as ordinal numbers and you need to quickly decode them into human-readable form. For instance, "2025, Day 200" corresponds to July 19, 2025.
Knowing what percentage of the year has passed can be surprisingly motivating or useful for planning. Our calculator shows you the current year progress as a percentage so you can see at a glance how much of the year remains. This is calculated by dividing the day number by the total days in the year (365 or 366) and expressing it as a percentage.
The calendar year is often divided into four quarters for business, financial, and academic planning. Q1 covers January through March (Days 1–90), Q2 covers April through June (Days 91–181), Q3 covers July through September (Days 182–273), and Q4 covers October through December (Days 274–365/366). Knowing which quarter a date falls in helps with reporting and goal-setting cycles.