Matthew Lincoln, PhD Cultural Heritage Data & Info Architecture

Convert EDTF to Regular Dates Without Needing to Code

TL;DR: I’ve made a small, in-browser utility for converting EDTF dates to pairs of date boundaries without needing to code.

A screenshot of the EDTF min/max calculator

A screenshot of the EDTF min/max calculator

Many readers of this blog will be familiar with the “preferred” way to specify dates for computers: ISO 8601, or YYYY-MM-DD, such as the date of this post, 2021-03-20.

This is great when you have an exact date you want to specify, but as is often the case in messy historical / humanisitc data, we rarely have such precision. We may only know, for example, that:

  1. a painting was made at some point in 1653
  2. a book was published on some day in August 1801
  3. a person of interest arrived at a city on April 2, 1930, and left sometime in November of 1934
  4. a probate inventory has only a partially legible date written on it: 1731-02-1…[something]

One strategy to deal with assertions like these when computing is to create a pair of YYYY-MM-DD dates representing the earliest and latest possible dates given our range of certainty. Thus:

  1. The painting was made between 1653-01-01 and 1653-12-31
  2. The book was published between 1801-08-01 and 1801-08-31
  3. The person was within the city at some time between 1930-04-02 and 1934-11-30
  4. The probate inventory was made between 1731-02-10 and 1731-02-19

With these boundaries, we can search through uncertain dates, visualize possible time ranges and overlaps with tools like Palladio, and more. But it is a tremendous pain to manage so many different columns during data entry and cleaning.

The Extended Date/Time Format (EDTF) Specification (core features of which are adopted by ISO 8601-2,) is an expressive update to the strict precision of ISO 8601-1, specifying notation for dates and date ranges of varying precision and certainty. From our examples above, we could succinctly write:

  1. 1653
  2. 1801-08
  3. 1930-04-02/1934-11
  4. 1731-02-1X

and tools / code libraries for parsing EDTF can understand each of these cases and compute the possible earliest/latest dates (along with many other properties) for further use in search, computing, or visualization. My EDTF converter lets you paste in a list of EDTF dates and it’ll calculate the earliest and latest date boundaries (as well as alert you if any of your date strings are invalid.)

There’s a lot more to EDTF than the examples shown here (including qualifications, seasons, open-ended intervals, and more) and the various parsing libraries can do more than pull out early/late date boundaries. I recommend you read more about the EDTF spec and try out the the Python or JavaScript EDTF libraries.

Comments are enabled via

Cite this post:

Lincoln, Matthew D. "Convert EDTF to Regular Dates Without Needing to Code." Matthew Lincoln, PhD (blog), 20 Mar 2021,

Tagged in: datadigital humanitiescode