What are custom calendars?

Edit Calendar - Months

By default, Aeon Timeline ships with an implementation of our standard Western Gregorian calendar, with 12 months in a year, 7 days in a week, and eras marked as BC and AD.

Aeon Timeline allows users to create their own custom calendars for use in projects. Uses for this include:

  • Changing the names of existing elements (e.g. using BCE and CE, or renaming weekdays and months to another language)
  • Re-creating other historic calendars such as the Julian calendar.
  • Creating your own fantasy calendar with your own fantasy world.

Editing Calendars

Calendars are created and edited as part of Timeline Settings. Once you have created your calendar, you can choose Save as Custom Template in Timeline Settings to save the edited template (including your calendar) as a new custom template option. It will then be available to choose for new projects in the Welcome screen.

Note that calendars can only be edited for new timelines. Once you add an event or entity to a timeline, you will no longer be able to edit the calendar.

Components of a calendar

When designing a custom calendar, it is composed of the same elements that are used in a standard calendar. As such, a calendar has the following components:


An era represents a block of years numbering from 1 to a maximum value. Eras can count forwards or backwards (starting from 1), and usually last for a specific number of years.

In all calendar systems, there must be one backwards era of infinite length, and one forwards era of infinite length (equivalent to our BC and AD) , so that any point in time can be correctly labelled. In some calendar systems these may represent pre-historic times and unknown future times.

Eras can be set to include “leap years”. These are calculated using the rules of our standard Western calendar (every 4th year except every 100th, but including every 400th).


Normally, this is used to represent the number of days for a planet to orbit the sun. However, in more general terms, this represents a number of days that are grouped together.

A year is composed of a number of months. You cannot set the duration of years directly, instead the duration of a year is determined by the sum of the days in all months.


A month is given a name (such as January), an abbreviated name (such as Jan), and a length in days for both normal and leap years.

In the standard calendar, months approximate the length of a lunar cycle, but in a custom calendar they could be used for other purposes, such as setting up a different month for each “season”.

Although all calendars must contain at least one month, you can setup a single month that lasts the duration of a year and effectively ignore the value, if desired.


In the standard calendar, a day represents the amount of time it takes for the Earth to rotate on its Axis (approximating the length of time between sunsets).

In creating a custom calendar, you can specify the number of hours in a day.

You can also specify the number of days in a week, and give a name (such as Monday) and abbreviated name (such as Mon) to each day.

To link your days with the rest of the calendar system, one day must be specified as the first day of the final era (this is the equivalent of specifying that the 01/01/0001 AD is a Monday).

All custom calendars must have at least one day, but if you do not wish to have separate weekdays, you can create a single weekday (called ‘Day’), and effectively ignore the value.

Hours, Minutes, Seconds

As mentioned above, the custom calendar allows you to specify the number of hours in a day.

Aeon Timeline does not allow you to customise units smaller than this. An hour will always be composed of 60 minutes, and a minute will always be composed of 60 seconds.


Bug reports? Suggestions? Feeling lost? Leave your questions or comments below…