Board Game Arena

Mathew5000 wrote: ↑08 February 2026, 17:08 I wonder if 2p games use "modern" Elo but 3p+ use "ancient" Elo. Also, in that old thread where Romain672 explained this, were we talking about a multiplayer game? If so, maybe there hasn't been any change made since then.

This could very well be the explanation. That old Kingdomino tournament from 2021 was multiplayer, and the January 2025 example I found above that used modern Elo was two-player.

Here's a couple of 2p Swiss tournaments from 2021 that I played:

• https://boardgamearena.com/tournament?id=94840

• https://boardgamearena.com/tournament?id=99315

In both cases, the "Opponents' average" column contains three-digit numbers which plausibly are the players' opponents' average Elo according to the "modern" system.

So based on this, I think we can tentatively conclude:

(a) For 4p games, a Swiss tournament uses the ancient (4-digit) system of Elo in the "Opponents' average" column.

(b) For 2p games, a Swiss tournament uses the modern (2-digit) system of Elo in the "Opponents' average" column.

(c) There has been no change to the above in the last five years.

Still to do: check some Swiss tournaments of 3p games (and I guess 5p games, 6p games etc.).

Mathew5000 wrote: ↑08 February 2026, 17:44Still to do: check some Swiss tournaments of 3p games (and I guess 5p games, 6p games etc.).

Here's a Swiss tournament for a 3p game (with one table each round being 2p): https://boardgamearena.com/tournament?id=337117 The standings use the "ancient" Elo (4 digits). So I guess it's only for 2p games that "modern" Elo is used. Someone should file a bug report I suppose, because it's rather odd, although I guess doesn't really affect very much.

Mathew5000 wrote: ↑13 February 2026, 05:42 Someone should file a bug report I suppose, because it's rather odd, although I guess doesn't really affect very much.

Other than using it for this purpose, why do they even need to track the old Elo at all? Is it used anywhere else?

It had to have been a conscious choice to switch to modern Elo for two-player games. So why was it decided that 3+ player games would be left on the old system?

All rhetorical questions, obviously, given that no one who actually knows the answers is going respond to this thread.

Meeplelowda wrote: ↑13 February 2026, 06:37

Mathew5000 wrote: ↑13 February 2026, 05:42 Someone should file a bug report I suppose, because it's rather odd, although I guess doesn't really affect very much.

Other than using it for this purpose, why do they even need to track the old Elo at all? Is it used anywhere else?

It had to have been a conscious choice to switch to modern Elo for two-player games. So why was it decided that 3+ player games would be left on the old system?

All rhetorical questions, obviously, given that no one who actually knows the answers is going respond to this thread.

I don't know the exact math involved, but the way old elo was calculated for multiplayer games may be more in line with how the swiss system works.

Meeplelowda wrote: ↑13 February 2026, 06:37 Other than using it for this purpose, why do they even need to track the old Elo at all? Is it used anywhere else?

I have now answered this question! Even if the second tie breaker is displayed in the modern Elo format, behind the scenes it is still calculated using the ancient Elo format. For example, see the values taken from the average_opponent_elo field of the final standings extracted from the JSON object holding the data for this tournament:
TheRealC: Rank 1, Points 10, Played 5, Avg Opponent Pts 6.4, Avg Opponent Elo 1481.2
BuzBuz: Rank 2, Points 8, Played 5, Avg Opponent Pts 5.6, Avg Opponent Elo 1473.8
Meeplelowda: Rank 3, Points 8, Played 5, Avg Opponent Pts 4.4, Avg Opponent Elo 1451.8
PingouPingou: Rank 4, Points 6, Played 5, Avg Opponent Pts 7.2, Avg Opponent Elo 1496
Rand-al-Thor: Rank 5, Points 6, Played 5, Avg Opponent Pts 5.6, Avg Opponent Elo 1521.2
Dan027: Rank 6, Points 6, Played 5, Avg Opponent Pts 5.2, Avg Opponent Elo 1499.2
Serkulle: Rank 7, Points 6, Played 5, Avg Opponent Pts 4.8, Avg Opponent Elo 1487.8
seb b: Rank 8, Points 4, Played 5, Avg Opponent Pts 6, Avg Opponent Elo 1512.4
DeeOne: Rank 9, Points 4, Played 5, Avg Opponent Pts 5.2, Avg Opponent Elo 1484
Raginis: Rank 10, Points 4, Played 5, Avg Opponent Pts 4.8, Avg Opponent Elo 1453.2
Juanar: Rank 11, Points 4, Played 5, Avg Opponent Pts 4.4, Avg Opponent Elo 1513.6
Bennozaurus: Rank 12, Points 4, Played 5, Avg Opponent Pts 4.4, Avg Opponent Elo 1506.4
Radix1214: Rank 13, Points 4, Played 5, Avg Opponent Pts 4.4, Avg Opponent Elo 1483.2
Gabyta_sc: Rank 14, Points 2, Played 5, Avg Opponent Pts 4.4, Avg Opponent Elo 1522.2
José Bruno: Rank 15, Points 2, Played 5, Avg Opponent Pts 4, Avg Opponent Elo 1473
Beliminorgath: Rank 16, Points 2, Played 5, Avg Opponent Pts 3.2, Avg Opponent Elo 1440.2

The calculated values are in the ancient format, but they are displayed in the modern format. So it seems no matter where Elo is shown in the UI it is still stored in the ancient format and just converted upon display to the modern format. I'm still working on confirming this using the Play Now page as an example.

Ah, very interesting! How are you accessing the JSON?

If I understand correctly, then there must be a simple formula to convert from ancient Elo to modern Elo. Are you able to say what the formula is?

Mathew5000 wrote: ↑24 May 2026, 17:06 Ah, very interesting! How are you accessing the JSON?

If I understand correctly, then there must be a simple formula to convert from ancient Elo to modern Elo. Are you able to say what the formula is?

It's part of the payload when getOverview.html is returned. I wrote instructions for how to get to it here. I discovered this technique when I was looking for a way to get a list of people who had registered for one of my completed tournaments so I could invite them to the next one because the recent tournament update removed the ability to copy/paste the list. [To BGA admins: I DO NOT automate the invites with a script; it's done manually.]

I was curious what the formula is, too. Chrome AI says it is ancient Elo -1300. Although that checks out if you visually compare the value for the ancient Elo with the value that's displayed, I could not locate a .js file that is doing the conversion. By the way, this was a tournament restricted to <300 modern Elo, which is why the Elos are so low for an abstract game.

Thanks. ChatGPT pointed me to this thread from 2017, which includes the "just subtract 1300" formula: viewtopic.php?t=10974 (also https://boardgamearena.com/news?id=319 ). ChatGPT noted that if someone's Elo under the old system was, say, 1380, then their Elo under the modern system might well be 100 (not 80) because if you've ever passed 100 you can't drop below it in the new system, although you could drop below 1400 in the old system.