About the Day of the Year Calculator
This day of the year calculator converts a calendar date into its day number — 1 for 1 January up to 365, or 366 in a leap year. It also shows how many days are left until the end of the year, what percentage of the year has passed, the ISO week number, the quarter, and the date in the compact YYYY-DDD ordinal format.
Day numbers are used in manufacturing and food lot codes, logistics and shipping labels, military and aviation date stamps, data files and scientific logs, where a single number is easier to sort than a month and day. They are also handy for tracking personal goals: day 100, a 365-day challenge, or how far through the year your budget should be.
In a leap year every date from 1 March onwards has a day number one higher than in a common year — 1 March is day 60 normally and day 61 in a leap year — so always check which year you are working in.
With the default inputs, the day of the year is 272. Change any value above to recalculate instantly.
How to use the day of the year calculator
- 1Pick the date you want to convert.
- 2Read the day number, days remaining and percentage of the year completed.
- 3Use the ordinal date (YYYY-DDD) for logs, lot codes or file names.
- 4Check the month table to convert other dates in the same year at a glance.
Formula and method
The day number is the sum of the lengths of the months before the date plus the day of the month. January has 31 days, February 28 (29 in a leap year), and so on. A year is a leap year if it is divisible by 4, except century years, which must be divisible by 400 — so 2000 was a leap year and 2100 will not be.
The percentage of the year completed counts the chosen day as finished: day number ÷ days in the year × 100. The ordinal date is written as the four-digit year, a hyphen and the zero-padded day number, as defined in ISO 8601.
- Day of year
- 1 for 1 January up to 365 or 366
- Days in year
- 366 in a leap year, otherwise 365
Worked examples
29 September 2026
January to August 2026 add up to 243 days; adding 29 gives day 272. With 365 days in 2026, 93 days remain and the year is 74.5% complete.
New Year’s Eve in a leap year
2024 was a leap year with 366 days, so 31 December 2024 was day 366 and no days were left in the year.
1 March 2028 (leap year)
January (31) plus a 29-day February gives 60 days, so 1 March 2028 is day 61. In a common year such as 2027, 1 March is day 60.
Frequently asked questions
What day of the year is it today?+
Enter today’s date to see it. For reference, 1 July is day 182 in a common year and day 183 in a leap year, and 31 December is day 365 or 366.
Is the day of the year the same as a Julian date?+
Informally, yes — many industries call the day-of-year number (often written YYDDD) a “Julian date”. Astronomers use Julian Date to mean a continuous day count since 4713 BC, which is different; use the Julian date converter for that.
How many days are in a year?+
A common year has 365 days and a leap year has 366. Leap years occur every year divisible by 4, except century years not divisible by 400, so 2028 is a leap year but 2100 is not.
What is day 100 of the year?+
Day 100 is 10 April in a common year and 9 April in a leap year. Day 256, celebrated as Programmers’ Day, is 13 September (12 September in leap years).