Find the day number within the year for any date

Count a date’s one-based position within its Gregorian year.

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ToolDay of Year
Input
Output
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How it works

UTC midnight for the selected date is subtracted from UTC midnight on 1 January, divided by 86,400,000 milliseconds, and increased by one. Remaining days subtract that ordinal from 365 or 366 under the Gregorian leap rule.

  • Counting begins at one, so 1 January is day 1.
  • UTC arithmetic prevents a 23- or 25-hour daylight-saving day from changing the ordinal.

Worked example

Find the day number within the year for any date
Find which day of the year March 15 is
Input
											2025-03-15
Output
												Date: 2025-03-15
Day of Year: 74 / 365
Days Remaining: 291
Year Progress: 20.27%
Leap Year: No

When to use this

Ordinal-date records encode values such as 2024-060, seasonal datasets index annual observations, and maintenance logs compare milestones without month names.

Edge cases

  • 31 December is day 366 in a leap year but day 365 in a common year.
  • A local timestamp near midnight is reduced to the parsed UTC calendar date.
  • An invalid date string is rejected rather than normalized into another month.

References