Imperial Dates And Events

Who would have thought WH 40k could be so educational? In writing any backstory, I wanted to fit the campaign into WH40k canon events and so became conversant with the Imperial Dating System at Lexicanum and many variations of contemporary dating systems.

It was kind of interesting not being able to find an online coverter to easily translate a calendar date and time into the decimal code, given the crunchy nature of the game for fanatics to take root in. And rather than give in to the near-heretical ideas of Roboute Guilliman and use a new numbering system, I set to task in identifying an easier method for date/time.

The imperial three digit date/time group (DTG) is somewhat problematic. We first thought this was simply the ordinal date (1 – 365) but in closer reading we discovered this was a calendar year divided into 1000 equal parts of about 8 hours and 45 minutes each.

First, we need the Ordinal Date between 1 and 365 (ignoring leap years), using the guide below as a handy reference:

To the day of	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sept	Oct	Nov	Dec
Add	0	31	59	90	120	151	181	212	243	273	304	334
Leap Year	0	31	60	91	121	152	182	213	244	274	305	335

Also obtainable from NASA’s J-Day Converter

We could simply multiply that number by three and call it a day, but that would yield a number up to 1095; an error factor of almost 10%! As we are looking for a year to be parts of 1000, we’ll ignore leap years and simply divide it out; or 365x = 1000 for a factor of ~ 2.73926.

So, using the table, a game taking place on October 5th would be 273 + 5 = 278; 278 x 2.73926 = 761.5. To make it a game taking place around 4PM, we’d round up and add 2 = 764!

This should be more than good enough to be accurate in a tabletop sense. To figure out what year we’re starting, I figure the Indomitus Crusade, the release of 9th and the reason most of us are hopping back in, takes place at 111.M42. We’ll take that to signify our current year is 111.M42 and future tracking will look like this:

764 111.M42 - A Battle Took Place.