Time & Date · Updated 2026

Day of Year Calculator

Find what day number of the year any date falls on, or look up the date for any day number. See how far through the year you are, plus days remaining.

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Day of Year Calculator
Date to day number and back

Select a date to find its day number, or enter a day number to find its date.

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What Day of the Year Is It?

January 1 is day 1 and December 31 is day 365, or 366 in a leap year. September 21, 2026 is day 264 of 2026, with 101 days left and 72.3% of the year behind us. Pick any date above to get its day number and ISO week, or switch tabs to turn a day number back into a calendar date.

Day Numbers Month by Month

The day number of the first and last day of each month. Common years such as 2026 and 2027 use the left columns; leap years such as 2028 use the right ones. The two only differ from March 1 onward.

Month1st (common)Last (common)1st (leap)Last (leap)
January131131
February32593260
March60906191
April9112092121
May121151122152
June152181153182
July182212183213
August213243214244
September244273245274
October274304275305
November305334306335
December335365336366

To find any date, take the "Last" figure for the month before and add the day of the month. September 21, 2026 is 243 (end of August) plus 21, which is 264. Day 256 (2 to the 8th power, celebrated by some as Programmers' Day) falls on September 13 in common years and September 12 in leap years.

ISO Week Numbers Explained

Week numbers used in business, payroll and manufacturing follow ISO 8601: weeks start on Monday, and week 1 is the week that contains the year's first Thursday (the same as the week containing January 4). That makes a year 52 or 53 weeks long, and a few days around New Year can belong to the neighboring year.

DateWeekdayISO week
Jan 1, 2026ThursdayWeek 1 of 2026
Sep 21, 2026MondayWeek 39 of 2026
Dec 31, 2026ThursdayWeek 53 of 2026
Jan 1, 2027FridayWeek 53 of 2026
Jan 4, 2027MondayWeek 1 of 2027
Dec 30, 2024MondayWeek 1 of 2025

2026 is a 53-week year because it starts on a Thursday. The next one is 2032, a leap year that also starts on a Thursday. The "ISO week" row in the results uses this standard, so it matches Excel's ISOWEEKNUM function and the week numbers used across most of Europe.

Reading Julian Date Codes

Manufacturers, the military and older mainframe systems often write dates as a year plus a day number, loosely called a Julian date. Split the code into year and day, then look the day up in the second tab.

CodeFormatCalendar date
26135YYDDDMay 15, 2026
2026264YYYYDDDSep 21, 2026
2026-264ISO 8601 ordinalSep 21, 2026
27045YYDDDFeb 14, 2027
26060YYDDDMar 1, 2026
28060YYDDDFeb 29, 2028

The last two rows show why the year matters: day 60 is March 1 in a common year but February 29 in a leap year. Some plants print only the last digit of the year (6264 for September 21, 2026), so check the packaging for a second date if the decade is unclear.

Method and sources. Day number equals the days in all complete months before the date plus the day of the month, with February at 29 days in leap years (divisible by 4, except century years not divisible by 400). ISO week numbers follow ISO 8601: weeks start on Monday and week 1 contains the first Thursday of the year. Every figure on this page was computed with those rules.
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Day of Year Questions

The day of the year (also called the ordinal date) is a number from 1 to 365 (or 366 in a leap year) that indicates which day of the year a given date falls on. January 1 is day 1, January 2 is day 2, and so on through December 31, which is day 365 (or 366 in a leap year). This numbering system is useful in astronomy, the military, agriculture, and computing where a single number is more convenient than a month-day combination.

Click the "Today" button in the calculator above to instantly find today's day number. For reference, May 15 is day 135 in a non-leap year and day 136 in a leap year. The calculator automatically accounts for whether the selected year is a leap year. January 1 is always day 1, and December 31 is always the last day (365 or 366).

Add up the number of days in all complete months before the target month, then add the day of the month. For non-leap years: January = 31 days, February = 28, March = 31, April = 30, May = 31, June = 30, July = 31, August = 31, September = 30, October = 31, November = 30. Example: March 15 = 31 (Jan) + 28 (Feb) + 15 = 74. In a leap year, add 1 to any date from March 1 onward. For programming, round instead of rounding down: day = Math.round((date - Jan1) / 86400000) + 1. With local times, the spring daylight saving change makes one day 23 hours long, so Math.floor would come out a day short.

Day 100 falls on April 10 in a non-leap year and April 9 in a leap year. After day 100, 265 days remain (266 in a leap year). Day 100 is sometimes noted as a milestone called "The 100th Day" in schools. Other common milestone days: day 1 = January 1, day 91 = April 1 (start of Q2), day 182 = July 1 (mid-year), day 274 = October 1 (start of Q4), day 365 = December 31.

A leap year has 366 days instead of 365, with February 29 added. Leap years occur when a year is divisible by 4, except for century years not divisible by 400 (so 2000 was a leap year, 1900 was not, and 2100 will not be). For dates from January 1 through February 28, the day number is the same in both leap and non-leap years. From March 1 onward, every date's day number is 1 higher in a leap year. December 31 is day 365 in a non-leap year and day 366 in a leap year.

In computing and the US military, the ordinal date format YYYY-DDD is used, where DDD is the day of the year. For example, May 15, 2026 would be written as 2026-135. This format is defined by ISO 8601 and is sometimes called the "Julian date" in computing contexts (distinct from the astronomical Julian Day Number). It is used in COBOL mainframe systems, US military logistics, food manufacturing expiration codes, and some EDI (Electronic Data Interchange) standards. Converting from YYYY-DDD to a calendar date requires the same calculation as our Day Number to Date mode.

Agriculture uses Growing Degree Days (GDD) and day-of-year numbers extensively. Planting schedules, frost dates, and harvest windows are often expressed as day ranges. For example, "plant corn after day 120" means after April 30 in a non-leap year. Weather stations record temperature data by day number for comparison across years. Last frost dates are expressed as the average day number of the last frost in a region, making it easy to count days to planting time regardless of which day of the week the date falls on.

Percentage = (day number / total days in year) × 100. In a non-leap year, July 2 (day 183) contains the midpoint: 183/365 ≈ 50.1%. In a leap year, July 2 (day 184) is also near the midpoint: 184/366 ≈ 50.3%. The exact midpoint of a common year is noon on July 2; in a leap year it is the stroke of midnight between July 1 and July 2. This calculator shows the year progress as a percentage bar in the results panel, updated for the exact date you enter.

Some commonly referenced day numbers in a non-leap year: Day 1 = Jan 1 (New Year). Day 32 = Feb 1. Day 60 = Mar 1. Day 91 = Apr 1 (start of Q2). Day 100 = Apr 10. Day 121 = May 1. Day 151 = Jun 1. Day 182 = Jul 1 (mid-year). Day 212 = Aug 1. Day 243 = Sep 1. Day 274 = Oct 1 (start of Q4). Day 305 = Nov 1. Day 335 = Dec 1. Day 365 = Dec 31. In a leap year, add 1 to any date from March 1 onward.

Food manufacturers often stamp a 3-digit Julian date (day of year) on packaging for lot tracking. A code of 135 means day 135 of the year. Switch to "Day Number to Date" mode, enter 135 and the year (usually the current year or the year printed alongside), and get the calendar date. Some codes use a 5-digit format: the first two digits are the year and the last three are the day. For example, 26135 = day 135 of 2026 = May 15, 2026. Canned and packaged foods often use this system.

2026 has 365 days, which is 52 weeks and 1 day. On the ISO week calendar used for business and payroll planning it has 53 weeks, because it starts on a Thursday. Week 53 runs from Monday, December 28, 2026 to Sunday, January 3, 2027, and week 1 of 2027 starts on Monday, January 4.

December 25 is day 359 in a common year such as 2026 and day 360 in a leap year such as 2028. Either way, 6 days of the year remain after Christmas.
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