The dwarven calendar is used to display the day, month, and year of any given date, and is visible in the upper right corner of the Status Screen ( ). There are 12 months in the dwarven year divided into 4 seasons of 3 months each. Unlike the traditional Gregorian calendar, each dwarven month is exactly 4 weeks long, or 28 days, for a total of 336 days in a year. New Year's Day and the first day of Spring both fall on the 1st of Granite. New Year's Eve and the last day of Winter both fall on the 28th of Obsidian. The months are named after kinds of stones, ore, gems and wood.
The game's first playable year begins whenever the world stops generating. By default, the world will stop genning at year 250. Worldgen can be set to stop at several distinct years ranging from 5 to 1050 when selecting Create a World, and can also be set to any arbitrary year by editing the advance option End Year in the Design New World with Advanced Parameters screen, or by interrupting world generation.
 Months and seasons
* If you are not at war with the Goblins then they will send caravans to you and you will be able to trade with them.
The seasons correspond to growing seasons from the farm plot menu, which dictate what can be grown when during the year. (See the list of crops.) It should be noted that crops grow during seasons regardless of the actual weather, so any crops that grow during the spring will do so regardless of how much rain your area gets.
Civilizations will visit your fortress based on what season it currently is. Trade caravans for each race show up during the specific seasons each year, with the elves arriving during the Spring, the humans during the Summer, and the dwarves during the Autumn. No caravans arrive for the winter (with the exception of goblins, if your civilization is at peace with them), so it's smart to stock up on food and drink during the fall (or autumn to those of you more educated people).
In addition to the year, a world's history is also divided into ages. An age can be seen as an epoch, something which defines the period of years it describes. The age itself has no bearing on gameplay other than as categorization in Legends mode, though players may witness a change in age (with an accompanied announcement) should their actions cause the current age to end. This may happen after killing a large number of megabeasts.
Ages are determined by the states of the world during world generation. Worlds start in the Age of Myth, though this may not always hold true if changes to world gen parameters are made. Some of the known things that influence the ages are number of megabeasts currently living and dominant civilizations. It is also possible for a world to enter a particular Age more than once (e.g., The Second Age of Legends) if the appropriate conditions are met.
 Known Ages
Below is a list of 'Ages' that may occur, an explanation and their (possible) triggers, and their in-game descriptions. World size may affect how long an age lasts. Because the age is dependent on variables such as number of megabeasts, number of civilized creatures, etc., smaller worlds will tend to change ages more frequently. Conversely, larger worlds tend to be more age-stable.
- Age of Myth, Age of Legends, Age of Heroes
Progression between these ages is most common in non-pocket worlds. The progression from Myth to Legends to Heroes is conditional upon the percentage death of megabeasts in a given world during generation. Slaying Megabeasts that visit you in Fortress Mode is known to trigger change of Age. In larger worlds, the proliferation (and extermination) of necromancers, vampires, and werebeasts during world generation can cause the age to regress back to Myth, sometimes multiple times.
- The Age of Myth was a time when living gods and mighty beasts still held sway.
- The Age of Legends was a time when the powers of the world were fading.
- The Age of Heroes was a time when the last of the powers fought their final battles.
- Age of (Megabeast's/Demon'sVerify/Titan's name/title)
Occurs mostly in pocket worlds, where there's one Megabeast, demon, or titan with a relatively large kill list.
- The Age of Flarrgh was a time when the titan Flarrgh was the only great power in the world.
- In case the creature itself hasn't got a relatively large kill list, but is mythical itself, the age may be named after the raceVerify:
- The Draconic Age was a time when the dragon Flarrgh was the only great power in the world.
- Age of (Megabeast/DemonVerify/Titan) and (Megabeast/DemonVerify/Titan)
Same as above, but with two notable Megabeasts/Demons. e.g.: "The Age of Roc and Dragon" or "The Age of Two Demons"
- The Age of Dragon and Demon was a time when the dragon Flarrgh and the demon Blarrgh were the only great powers in the world.
- Age of Three Powers
Even better than above, three notable Megabeasts, DemonsVerify, or titans.
- The Age of Three Powers was a time when the dragon Flarrgh, the demon Blarrgh and the titan Glarrgh were the only great powers in the world.
- Age of (Race name)
One race becomes dominant in the world, or it's the only race left in the world. e.g.: "The Age of Dwarves"
- The Age of Dwarves was a time when dwarves ruled the world.
- The Golden Age
Civilizations are expanding, and there are no wars and other things for them to worry about. This age is very common in pocket worlds, and naturally progresses from an age of a prominent figure.
- The Golden Age was a time when various civilized races peopled the world.
- Age of Fairy Tales
Toady One' quote from 2008 devlog:
"I finally saw a world arrive at the Age of Fairy Tales, which happens if mundane creatures (ie humans) make up at least 90% of the world's civilized population with the requirement that there are still a few fantasy creatures lurking around. In this case, it was a kobold cave that their scouts never found. I guess all of the fairy tales were about people having their crap stolen."
- The Age of Fairy Tales was a time when fantastic creatures were few and far between, and some even doubted their existence.
- Age of Twilight
There are no wars and other worries, but civilizations are too weak to expand or are crumbling apart.
- The Twilight Age was a time when fantastic creatures no longer lived in great numbers.
- Age of Civilization
Seems to be triggered when the world is mostly occupied by civilizations and there's no more fanciful creatures around.
- The Age of Civilization was a time when fantastic creatures were but mere stories told by travelers.
- Age of Death
The Age of Death is a time when there are no civilizations left alive. A world that ends generation in this age will only allow games to be started in Legends mode or Adventurer mode.
- The Age of Death was a time after civilization had crumbled completely.
- Age of Emptiness
The Age of Emptiness is a time when there are no civilized beings left alive. A world can be permanently locked in this Age if the number of civilizations, megabeasts, and titans are all set to zero during worldgen. A world that ends generation in this age will only allow games to be started in Legends mode or Adventurer mode.
- The Age of Emptiness was a time when no civilized peoples existed in the world.
- The Age of Emptiness was a time when only simple creatures inhabited the world.
Information taken from this Bay12 forum thread
A change in the season will generate an announcement. Depending on the biome your fortress is in, the announced season may be different from the calendar season. For example, in some biomes "wet" and "dry" seasons replace spring or summer. A few biomes lack any change in weather and those biomes announce a change of season by "-season- has arrived on the calendar." Regardless, plants and caravans always follow the calendar season listed on the status screen.
|World Generation (Basic / Advanced / Rejections)|
|Regions - Climate - Surroundings - Map legend|
|Civilizations - Sites ( Cave - Town - Fortress - Ruin ) - Calendar|
|Aquifer - Brook - Island - Tunnel - Volcano - Waterfall|
|Biomes||Chasm/Caverns - Desert - Forest - Glacier - Grassland - Lake - Mountain - Murky pool - Ocean - River - Savanna - Shrubland - Tundra - Wetland|