I am new to Forgotten Realms and I'm running the Tomb of Annihilation module. What year is it at the start of the adventure? Is there an official calendar someplace? Thanks!
The current year is not specified in the module anywhere and, for the purposes of the adventure, doesn't matter. Tomb of Annihilation happens more-or-less in a vacuum, no references are made within the module to events of other modules, and no novels have been released related to it. If there is a particular year that you like the idea of using, then go for it.
However, if you want to make sure you are in the right ballpark with regard to other published adventures, it would probably be somewhere after 1492DR. Thus far, every 5E storyline that has been dated has happened within the late 1480s (post-second-sundering) to early 1490s. This gives us a basic date range to consider
The second sundering, which is the event that moved us into 5E, ended in 1487 DR. This is our starting point.
The Tyranny of Dragons storyline takes place in 1489 DR.
Princes of the Apocalypse happens in 1491 DR
The plotting to set Out of the Abyss into motion got started around 1485/6 DR (according to a related novel: Archmage), but the actual events were said to happen right around the same time as ToD and PotA (per Chris Perkins)
The year for Storm King's Thunder is not set, but it makes references to Tyranny of Dragons as a past event. The phrasing implies this was relatively recent. Furthermore, there is a moment (p34) where...
Cultists from the Cult of Elemental Air turn up looking for allies. But the Elemental Cults are basically obliterated at the end of PotA...
So it seems that Storm King's Thunder is happening right about the same time as PotA.
The effects of the Soulmonger are very, very significant...so we know that ToA did NOT occur during the events of any of these prior adventures.
Thus, since the events of the world are fairly well booked from the second sundering up through 1491/2ish DR...if you want to slap a date on Tomb of Annihilation that makes sense with the other published adventures...then give it a date post-1492 DR
The exact year isn't listed in the module, as mentioned. But we can get a good idea of when it takes place. I'm looking specifically at the "History of Omu" section in Chapter 3, so, spoilers ahead for players.
First, the module says that "the Omuans' greed and hubris angered the god Ubtao, causing him to turn his back on Omu two hundred years ago--long before he abandoned the rest of Chult." The people of Omu needed new deities, so they turned to the Nine Gods, "for nine decades," after which point,
Omu drew the attention of Acererak, and "a little over a century ago, Acererak entered Omu and slew all nine trickster gods."
Now we skip ahead a bit. The module states that 50 years ago, the yuan-ti were banished from Hisari and came to Omu. At this point, "earthquakes shook Omu and cracked it open like a fig." Of course, earthquakes can appear whenever, but since Omu was a great civilization, they mustn't have had many this size. SCAG (The Sword Coast Adventurer's Guide) notes that the Second Sundering, which resulted in earthquakes and other disasters, began with the birth of the god Bhaal, in Balder's Gate in 1482 DR (the standard way of counting years in the Realms). Two years later, a series of calamities shake Faerun. It makes sense to place the Omuan earthquake around that time (~1484 DR).
But there is one more factor to consider: the Spellplague. This occurred in 1385DR, and during this time magic went haywire. This is guesswork, but if I were
I wouldn't do it then. So
Acererak must have arrived and slaughtered the Nine Gods before 1385DR
The most recent year mentioned in SCAG is 1487, so let's guess it's a little after that, say, 1493. That means Ubtao abandoned Omu around 1293, and the Omuans worshiped the Nine Gods until around 1383, which is "a little over a century ago," as required (see spoiler). This also means that the yuan-ti entered Omu around 1443. The yuan-ti are described as building their temple prior to the earthquakes, which lines up with this reasoning (since the earthquake probably took place during the Second Sundering).
Logic check. Current year: 1493. 1293, Ubtao abandons Omu. Omuans worship the Nine Gods until 1383, just before the Spellplague. The yuan-ti entered Omu in 1443, plenty of time to build even an elaborate temple before the earthquake in 1484.
It's a bit tight, but I think that timeline makes sense.
I think it happens right before Storm King's Thunder because of the Ring of Winter.
The Ring of Winter is with a man named Artus Cimber in Tomb of Annihilation. In Storm King's Thunder, the ring is given to a kid by his father, Artus Cimber. It can't be a coincidence.
According to page 92 of the ToA adventure book:
Fifty years ago <…> The evil warlord Ras Nsi, who had raised an army of undead to wage war on the holy city of Mezro, only to suffer a terrible defeat, arrived in Omu shortly after the yuan-ti.
It means that
50 years ago Mezro was still here and there were no Spellplague. But now Mezro is gone. As long Spellplague was in 1385 DR,
so ToA happens near 1435 DR.