This whole month is time month in celebration of the new year, so it's about time we actually talked about years. At the time of writing this it's the year 2017 A.D. So let's talk about that.
We talked about what a year is in a previous article but what we haven't touched on is the counting of years. 2,017 years ago, by the Gregorian Calendar was the year...1 B.C. There is no year 0. Of course the whole B.C and A.D thing didn't really come about until around 500 A.D, and wasn't popularized for more than 300 years from there. BC and AD have strong religious context, and so many people use the term CE for common era, as a religion neutral way of denoting the year. Others just leave theletters off entirely since context usually helps us differentiate between yesterday and a day over four thousand years ago without needing notation. But when it comes to what year it is in your campaign setting you should consider the 5 W's:
When is it?
This seems an easy question, you really just need a number and maybe a notation. It could be the year 500 FFF, or the year 4500, or the year 7 R.Q.N . Pick something that feels and sounds right for your game, and then get ready to explain it.
What does it mean?
Now we unpack things a bit more. If your calendar says it's year 500 FFF then it adds a lot of context to when you denote that "FFF" stands for "From first fire" which marks the first time humanity used fire as a tool. If it's just the year 4,500 that might mean it's been four and a half thousand years since someone started keeping track. But Year 7 R.Q.N might be the seventh year in the "Reign of Queen Nander" and perhaps new notations are included for every new reigning king or queen.
Why use this?
What makes this method of tracking the years any better or worse than any other? Or more realistically, which big shot decided to use this method above the superior ones? Some are rather self explanatory, and usually revolve around some big major event. Other methods are adopted when two or more very distinct cultures join together and they have to find some common ground to start counting from. Or in some cases a single, relatively small nation has their method of tracking years gradually mimicked by all other societies to facilitate trade and communication.
How is this tracked?
Imagine a society where every year in the Dwarven capital a 5 ft slab of stone is set atop a neat pile making a slowly growing column. Perhaps each new Era is marked by when that stone tower falls over. Some epochs, like those where an earthquake or other cataclysm occurs, are short and distinct because the stone tower is knocked over prematurely, while times of peace may be many many times longer in scale. Other methods are simpler, like measuring the reign of a monarch or particular council of elders.
Who uses this?
The alien entities visiting a post apocalyptic world are probably not going to consider it the year 86 S.B.D (Since Bombs Dropped), they'll probably have their own way of counting time. Likewise the Dark Elves probably don't care what or who Queen Nander is, and an ancient sorcerer from another reality might have been counting years since the dawn of time. So be sure to have a few backup methods of counting years for these other civilizations.
Hopefully this was helpful in thinking through the years in your setting, and if you need help naming those years and epochs than keep an eye out for an upcoming article about naming pieces of time!