Day of Year to Date Converter
How to use day of year to date converter
- Enter the calendar year.
- Enter a day number starting at one for January 1.
- Calculate and inspect its calendar date and ISO week.
Convert a year and ordinal day number into a validated calendar date.
How the result is calculated
The calculator validates the required dates, units and range before producing a result. Keep the inputs and the selected convention with the output so another person can reproduce it.
Read all calculation conventionsHow to read your result
Keep the inputs and conventions beside the answer. These values explain what the result measures.
| Result field | Meaning |
|---|---|
| Calendar date | January 1 advanced by day number minus one. |
| Day/year total | The selected one-based day and the year’s valid 365- or 366-day limit. |
| ISO week label | The same date expressed using its week number and week-year. |
A leap day changes later ordinal dates
Day 60 is March 1 in 2027 and February 29 in 2028. Day 366 is valid only in a leap year.
Try the example in the calculator above. Change one input at a time and compare the target, interval and selected rules. For a longer explanation read Convert ISO Week Dates and Ordinal Days to Calendar Dates.
Conventions to keep with your result
Ordinal dates use the selected Gregorian calendar year. A day number by itself does not identify a date; the year remains essential.
Day of Year to Date Converter: frequently asked questions
Does the first day use zero or one?
January 1 is day one.
Can day 366 be used in a common year?
No. The converter rejects it.
Is an ordinal date an ISO week date?
No. Ordinal dates count days within the calendar year; ISO week dates use a week-year, week number and weekday.
Learn the method
All guidesISO Week Numbers: Week 1, Week-Years and 53-Week Years
Find the ISO week-year near New Year and understand why January dates can belong to the preceding week-year.
Convert ISO Week Dates and Ordinal Days to Calendar Dates
Convert week-year/week/weekday values and year/day-number values correctly. Examples cover week 53, New Year boundaries, leap days and invalid inputs.
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