OmniCalcsDay of Year Calculator
Find the ordinal day of any date — January 1 is day 1, December 31 is day 365 (or 366).
How to Use This Calculator
Pick any date to see its position in the year, or enter a year to list every date with its ordinal day. Useful for date serials, logging and milestones.
- Leap years (divisible by 4, except century years not divisible by 400) have 366 days.
- Ordinal dates are written like "Day 147 of 2026".
Frequently Asked Questions
What is an ordinal date?
The day count within a year, starting from 1 on January 1. ISO 8601 formats it as YYYY-DDD.
How do I know if a year is a leap year?
A year is a leap year if divisible by 4, except century years — which must also be divisible by 400. So 2024 is a leap year, 2100 is not.
Why is my day-of-year number one higher on Feb 29+?
Leap years insert Feb 29 before the rest of the year, so every date after Feb 28 is shifted by one day.
Where is this commonly used?
In logs, science data, "day of year" sensors, and ordering dated files — for example, "day-182-report".
Practical Example
July 4, 2026 is day 185 of 2026. Adding the days of the months before July gives 31 (Jan) + 28 (Feb) + 31 (Mar) + 30 (Apr) + 31 (May) + 30 (Jun) + 4 = 185. Since 2026 is not a leap year, the year has 365 days, leaving 180 days until December 31.
- In the leap year 2024 the same date was day 186, one higher because of February 29.
What Your Results Mean
- Day X of 365/366 — the date's ordinal position in the year, starting at 1 for January 1.
- Days remaining — the full days left until the end of the year, not counting the current day.
- Weekday — the day of the week, useful when ordinal dates appear in logs, reports, or file names.