Creating Calendars

This page covers everything you need to build a calendar in MythTapestry — from a simple twelve-month structure to a fully original time system with custom eras, irregular months, and world-specific date formats.

Core concepts

Temporal scales

A calendar is built from temporal scales — the named levels of your timekeeping system. Year, Month, Day, Season, and Week are all examples of temporal scales. You define as many as your world needs, and each one has a type that controls how it behaves.

Scale type	Purpose	Examples
Hierarchical	Nested time divisions, from large to small	Year → Month → Day; Age → Cycle → Beat
Overlay	A repeating cycle that runs across the hierarchy	A 7-day week; a moon phase cycle; a market cycle
Subdivision	Time within a single day	Hour, Minute, Second; Bell, Quarter; Watch, Glass

Hierarchical scales

Hierarchical scales form the backbone of your calendar. They nest from large to small — a Year contains Months, which contain Days. You build this structure by linking each scale to its parent. The largest scale (Year, Era, or whatever you call it) sits at the root and has no parent.

At each level, you can define named units — the individual entries within that scale. The Month scale might have 12 named units: January through December, each with its own length in days. Scales without named units, like Year, simply count forward as numbers.

Overlay scales

Overlay scales repeat on their own cycle, independent of the months and years around them. A seven-day week is a good example: it rolls forward without caring where month boundaries fall. To define an overlay, you need three things:

• Cycle length — how many units in one complete cycle (e.g. 7 for a week)
• Cycle base unit — what the cycle counts in (days, for most cases)
• Anchor point — a specific day and which overlay unit it falls on (e.g. “the first day of Year 1 is a Monday”)

The anchor tells MythTapestry where the cycle begins on your calendar. Without it, the overlay has no fixed starting point.

Subdivision scales

Subdivision scales break a day into smaller units: hours, minutes, seconds, or their equivalents in your world. They work inside a single day, separate from the date structure. See Time & Subdivisions for the full guide.

Temporal units

Each hierarchical or overlay scale can contain units — the named entries within it.

Property	Description
Name	The full label for this unit (e.g. “January”, “Monday”, “First Quarter”)
Abbreviation	A short form for compact display (e.g. “Jan”, “Mon”)
Ordinal	The unit’s position within the scale, counting from zero
Unit length	How many days this unit spans (for day-level hierarchical units)
Is variable	Check this if intercalation rules can change this unit’s length (e.g. February)

Units without a name are displayed as numbers: “Month 3”, “Day 45”. Named units appear as their name in formatted output.

Intercalation rules

Intercalation handles irregular adjustments to your calendar — extra days inserted periodically to keep it aligned. Leap years are the most familiar example.

Each intercalation rule has:

Property	Description
Every N cycles	How often the rule fires (e.g. every 4 years)
Except every M cycles	Skip the rule at this interval (e.g. except every 100 years)
Re-include every P cycles	Override the exception (e.g. apply again every 400 years)
Targets	What changes when the rule fires

Each rule applies one or more targets:

Target type	What it does	Example
Extend unit	Add days to an existing variable-length unit	Add 1 day to February
Insert period	Insert a standalone period at a fixed position	Insert “Epagomenal Days” after day 360

Example — Gregorian leap year:

Every 4 years → extend February by +1 day
  Except every 100 years → skip it
  Except-except every 400 years → apply it anyway

This produces the familiar 365/365/365/366 pattern, with century years non-leap except those divisible by 400.

Tip

The Gregorian preset includes these two rules already configured. If you’re building a custom calendar with leap years, open the Gregorian preset and use its intercalation rules as a reference.

Format tokens

Format strings control how dates display in your world. You build a format string from format tokens, each written as:

{ScaleName:formatter}
{ScaleName:formatter:padding}

ScaleName is the name of any temporal scale in your calendar (e.g. Year, Month, Day, Week, Season). formatter picks what to show. padding zero-pads the output to a minimum width.

Available formatters:

Formatter	Output	Example (Month scale, January)
value	The numeric value at this scale	{Year:value} → 2024
num	1-indexed number	{Month:num} → 1
unit	Full unit name	{Month:unit} → January
abbr	Abbreviated unit name	{Month:abbr} → Jan
day	Day within the current unit, starting at 1	{Day:day} → 15
day_ord	Day with ordinal suffix	{Day:day_ord} → 15th
sub_unit_name	Custom day name from a unit’s sub_unit_names list (e.g. Roman day names)	{Month:sub_unit_name} → Kal.

Padding (optional third segment): :02 pads to at least 2 digits with a leading zero, :04 to 4 digits.

Format string examples:

Format string	Displays as
{Month:unit} {Day:day_ord}, {Year:value}	January 15th, 2024
{Year:value:04}-{Month:num:02}-{Day:day:02}	2024-01-15
{Week:unit}, {Month:abbr} {Day:day}	Monday, Jan 15
{Season:unit} {Day:day_ord}, Year {Year:value}	Spring 23rd, Year 1542
{Month:sub_unit_name} of Year {Year:value}	Kal. of Year 2024

Any text between tokens is kept as-is. Create as many format strings as you like and mark one as the default. The default format is what the app uses when displaying dates throughout your world.

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Creating a calendar

1. Go to Management > Calendars in the world sidebar.
2. Click Create Calendar.
3. Choose a preset — Gregorian, Lunar, or Custom — as your starting point.
4. Enter a name and optional description for the calendar.
5. If this calendar covers your whole world (rather than a specific region or culture), toggle Global on.
6. Review the structure preview showing your temporal scales.
7. Click Customize Structure to add, edit, or remove scales, units, and intercalation rules.
8. Review and edit format strings to control how dates from this calendar display.
9. Save the calendar.

Note

Presets load a fully configured calendar you can use immediately. You only need to open the customisation sections if you want to change something.

Calendar fields

Field	Required	Description
Name	Yes	A unique name for this calendar within your world
Description	No	Notes about this calendar’s cultural or historical context
Days per year	Yes	The total number of days in a standard year before intercalation (e.g. 365, 354, 360)
Global	No	Whether this calendar applies world-wide or only to a specific region or culture
Epoch description	No	A label for what Year 1 represents (e.g. “Years since the Founding”, “After the Sundering”)

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How calendars apply across your world

MythTapestry uses a simple priority system to decide which calendar applies where:

World default calendar
  └── Content unit override (a chapter set in a different culture)
        └── Inline date mark override (a single date mention in your prose)

• World level: The calendar you designate as global is used everywhere by default — events, entity fields, and date references all inherit it.
• Content unit level: Each chapter or scene can override the calendar if the narrative takes place in a culture that uses a different one.
• Inline mark level: Individual date references in your writing can specify their own calendar, overriding both the world and content unit defaults.

Tip

If your world uses only one calendar, ignore this entirely — everything uses the world default automatically.

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Linking two calendars

If your world has multiple calendars, you can establish a calendar reference date to align their timelines. You specify one date in Calendar A and the equivalent date in Calendar B. From that anchor, MythTapestry can convert any date in either calendar to the other.

Example: “Year 1 of the Imperial Calendar is the same day as Year 433 of the Old Calendar.” After setting this reference, a date entered in the Imperial Calendar automatically shows its Old Calendar equivalent wherever both are relevant.

1. Go to Management > Calendars.
2. Open the calendar you want to align (the source calendar).
3. Click Link to another calendar.
4. Choose the target calendar — the one you’re aligning with.
5. Enter the source date in the source calendar’s own notation.
6. Enter the target date — the matching date in the target calendar.
7. Add an optional description (e.g. “Imperial Year 1 = Old Calendar Year 433”).
8. Save the reference.

After linking, date conversion between the two calendars is automatic.

Note

Removing a calendar reference does not undo the alignment. If you want to fully disconnect a calendar, reset its epoch manually from the calendar settings.

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What the Gregorian preset includes

• Hierarchical scales: Year → Month (12 named units, January–December, with variable lengths) → Day
• Overlay scale: Week (7-day cycle: Monday–Sunday)
• Subdivision scales: Hour (24 per day) → Minute (60 per hour) → Second (60 per minute)
• Intercalation: Two rules implementing the standard Gregorian leap year pattern
• Format strings: ISO 8601, Long Date, Date & Time, Weekday Date, and Short Numeric

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Building a custom fantasy calendar: example

Here is a complete structure for a fantasy world with seasonal months and a ten-day week:

Scale	Type	Structure
Era	Hierarchical (root)	Numeric counter; no named units
Year	Hierarchical	Numeric counter; 360 days
Season	Hierarchical	4 named units: Spring, Summer, Autumn, Winter (90 days each)
Day	Hierarchical (leaf)	Numbers 1–90 within each season
Tenday	Overlay	10-day cycle with units: Firstday through Tenday
Hour	Subdivision	24 per day
Minute	Subdivision	60 per hour

A format string for this calendar:

{Tenday:unit}, {Day:day_ord} of {Season:unit}, Year {Year:value} of Era {Era:value}

Displays as: Sixthday, 23rd of Summer, Year 1542 of Era 3