Convert tools

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.

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

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

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

FAQ

Day of Year Converter — What are the supported inputs and limits?

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

Format references

Tool page updated: