Day of the Year Calculator
About Day of the Year Calculator
What Is a Day of the Year Calculator?
A day of the year calculator converts a standard date into its ordinal day number within the year. January 1 is day 1, February 1 is day 32, and December 31 is day 365 (or 366 in a leap year). This ordinal date format is used in astronomy, meteorology, military operations, supply chain management, and data science where sequential day numbering simplifies calculations and comparisons.
How It Works
The calculator sums the days of all complete months before the target month, then adds the day of the month. For example, March 15: January has 31 days + February has 28 (or 29) + 15 = day 74 (or 75). It also calculates the remaining days until year end and the percentage of the year that has passed.
How to Use This Calculator
Enter any date and click Calculate. The result shows the day number (1-365 or 1-366), the number of days remaining in the year, the percentage of the year completed, and which quarter of the year the date falls in.
Frequently Asked Questions
What is the ordinal date format?
The ordinal date format uses the year followed by the day number, like 2024-074 for March 14, 2024. It is an ISO 8601 standard format commonly used in scientific and technical fields.
Is day 1 January 1 or January 0?
January 1 is always day 1. The numbering starts at 1, not 0. December 31 is day 365 (or 366 in leap years).
How does this differ in a leap year?
In a leap year, dates from March 1 onward have a day number one higher than in a non-leap year. The last day of the year is day 366.
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