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Day of Year Converter

Convert dates to year-and-ordinal-day notation or restore dates from ordinal days.

Convert in your browser · No sign-up

Uses YYYY-DDD with 001-based days and Gregorian leap-year rules. Invalid day 366 values are rejected.

Up to 100,000 UTF-16 units per input and 1,000,000 per result. See the supported formats and examples below.

Result

Add your input or load an example, then run the tool. Your result will appear here.

How to use

  1. Convert dates to year-and-ordinal-day notation or restore dates from ordinal days.
  2. Choose the mode or options, then run the tool.
  3. Review the result, then copy or download the TXT file.

Example

2024-12-31 ⇄ 2024-366

Details and limitations

Text stays in your browser; it is not sent to a conversion server.

Format references

Tool page updated: