Eras and regnal years

Eras are the most flexible part of a calendar. They’re PostRoll’s answer to Dale Reckoning, Sundering Reckoning, Year 12 of the Reign of Mira, After the Fall, and Pre-Divergence all at once.

Each era in the calendar editor has five meaningful settings, shown here as a compact example:

{
  "id": "second-age",
  "name": "Second Age",
  "short_name": "SA",                       // short label shown in dates
  "start_year": 1,                          // first year of the era
  "display_year_offset": 0,                 // optional — see below
  "year_format": "{year} {yearLabelShort}"  // optional — overrides the calendar's display format
}

How eras are matched

For any event with a year, PostRoll picks the era with the largest start year that’s still on or before that year. There’s no explicit end date on an era — each era runs until the start of the next.

So if your calendar has eras starting at year 1 and year 540:

Year 1 → first era.
Year 539 → first era.
Year 540 → second era.
Year 1247 → second era.

Eras are sorted by start year automatically; the order you add them in the editor is irrelevant.

How the start year works

The start year is the first year of the era — an era begins exactly on that year.
Negative values are fine — useful for “Before the Fall” eras that start at year -812.
Don’t give two eras the same start year. PostRoll will still pick one, but which one isn’t something to leave to chance, and the editor won’t warn you.

The year offset for regnal years

The trick that makes regnal calendars work. When you set a year offset on an era:

The underlying year keeps marching forward across era boundaries (so each event’s position on the master timeline stays consistent).
The displayed year is the underlying year minus the offset.

Example: a Reign of Mira era starting at year 1235 with a year offset of 1234 makes:

Year 1235 → displayed year 1.
Year 1240 → displayed year 6.
Year 1247 → displayed year 13.

The reset year number is available as the {year_in_era} token in the year format — see below.

Year format overrides

When you set an era’s year format, it replaces the calendar’s overall Display format for events in that era. This is what produces “Year 12 of the Reign of Mira” instead of “1247 SR”.

A few useful templates:

Template	Shows as
`{year} {yearLabelShort}` (default)	`1247 SR`
`Year {year_in_era} of the {eraName}`	`Year 12 of the Reign of Mira`
`{year_in_era}{eraShort}`	`12RM`
`Year {year_in_era}`	`Year 12`
`{day} {monthName}, {year_in_era} of the {eraName}`	`12 Brightember, 12 of the Reign of Mira`

The full token list is on Building a calendar.

Multi-era calendars

A calendar can have any number of eras. The Forgotten Realms typically has DR (Dale Reckoning) but might add NR (New Reckoning) or CR (Cormyr Reckoning) for sub-era history. Each era can have its own year offset and year format.

Players can switch eras mid-campaign — when the campaign reaches a historical inflection point, add a new era with a higher start year. Existing events keep their authored dates; events in the new era show with the new format.

Collapsing an era by default

There’s a setting to collapse an era by default, reserved for a future polish pass — the era editor accepts it, but the Timeline canvas and the Chronicle don’t act on it yet. You can still fold an era out of view by hand on the Chronicle tab (click the era heading); the canvas always shows every era band.

Worked example: dual-era post-apocalyptic

A “After the Fall” setting with two eras:

[
  {
    "id": "before-fall",
    "name": "Before the Fall",
    "short_name": "BF",
    "start_year": -2000,
    "display_year_offset": 0,
    "year_format": "{year} {yearLabelShort}",
    "is_collapsed_by_default": true
  },
  {
    "id": "after-fall",
    "name": "After the Fall",
    "short_name": "AF",
    "start_year": 1,
    "display_year_offset": 0,
    "year_format": "{year} {yearLabelShort}"
  }
]

Events authored in year -1340 show as “-1340 BF” (reading as “1340 years before the Fall”); events in year 127 show as “127 AF”.

Or: invert the BF year by setting the year offset to year + 1 to get “660 BF” for year -660, reading more naturally.