---
title: Historical Dates
description: How to enter dates — exact, approximate, uncertain, ranges, or unparseable — and how Preservated interprets them.
section: reference
order: 2
updated: 2026-06-12
verified: 2026-06-12
related: [guides/working-with-artifacts]
features: [historical-dates]
---

# Historical Dates

A reference for entering dates on artifacts, from precise timestamps to "sometime in the late 19th century" to expressions no date system can parse.

## Just type what you know

The date field accepts natural language. Preservated keeps **exactly what you typed** as the display text, and — when possible — also derives a formal machine-readable date behind it (using [EDTF](https://www.loc.gov/standards/datetime/), the Library of Congress standard for uncertain and approximate dates).

| You type                     | Interpreted as          | Behaves like              |
| ---------------------------- | ----------------------- | ------------------------- |
| `March 15, 1923`             | `1923-03-15`            | An exact day              |
| `April 1985`                 | `1985-04`               | Any day that month        |
| `circa 1920`                 | `1920~` (approximate)   | Around 1920               |
| `1920s`                      | `192X` (decade)         | 1920–1929                 |
| `late 19th century`          | `18XX`-range            | Roughly 1867–1900         |
| `between 1850 and 1900`      | `1850/1900` (interval)  | Anywhere in the range     |
| `1923?`                      | `1923?` (uncertain)     | Probably 1923             |
| `before 1940`                | `/1940` (open start)    | 1940 or earlier           |

## Unparseable dates are fine

Some dates are meaningful to your institution but can't be formalized:

- "Post factory closure"
- "After the big flood"
- "During the war years"

Type them anyway. They're stored faithfully and displayed as-is — they just won't participate in date filtering or timeline placement. The editor indicates when a date couldn't be parsed so you know which case you're in.

## How approximate dates behave

Two ranges are computed from every parseable date:

- **Strict bounds** — the tightest range the date can mean. `circa 1920` strictly means 1920.
- **Search bounds** — expanded for discovery. A search for "1918–1922" should find a photo dated `circa 1920`, so its search range stretches several years on each side.

Date filters and the timeline use search bounds; that's why a "1920s" filter surfaces items dated "circa 1930" near the boundary — by design, since approximate dates are honest about their fuzziness.

Approximate and uncertain dates are marked in the interface (for example "c. 1920") so visitors know the precision.

## Tips for clean data

:::tip
Prefer "circa 1920" over "1920" when you're guessing — an honest approximation filters better than a false precision, and AI date analysis follows the same convention.
:::

- One date field per artifact: if you know a range ("taken during the 1936–1937 school year"), enter the range rather than picking an endpoint.
- Imported dates are parsed the same way; the original source string is always preserved unmodified alongside the interpretation.