Edit Calendar Window

What are custom calendars? 

Aeon Timeline will, by default, use a standard Western Gregorian calendar with 12 months in a year, 7 days in a week and eras marked as BC and AD. However, you are also able to create your own custom calendar for use in projects if you wish. Uses for custom calendars include:

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

Editing Calendars

To edit the existing calendar:

  1. Open the Timeline Settings window by clicking the settings icon ( ) in the toolbar.
  2. In the Calendar & Date tab, click on Edit Calendar

Note that calendars can only be fully edited for new timelines. Once you add an event or entity to a timeline, you will still be able to edit the names associated with your months, weekdays and eras, but you will not be able to edit properties that affect calendar calculations.

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 numbered 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’. By default, these are calculated using the rules of standard Western calendar (every 4th year except every 100th, but including every 400th).

In the Eras tab, click on Customize leap years to change how these leap years are calculated.


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 an 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. 

Saving Custom Calendars

Once you have customized your calendar, you can choose Save as Custom Template in Timeline Settings. This allows you 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.