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Math Trades

If this in any way scares you then try a "mock" math trade, see
Mock Math Trades - Learn to be a math trader

Thanks to Lindsey for putting together this cool guide for Math trades, the original content of this Wiki entry was taken from Math trade guide.

Math trades are a very good way to swap games with other people on BoardGameGeek. But with all the posts in your average trade, they can be hard to follow if you're new to them. I've tried here to describe how to (and whether to) participate in math trades, and hopefully to take care of any confusion about them.

If, on the other hand, you're interested in running a math trade, I recommend a look at Regai's post on the subject, at Math Trade Moderators Guide (Last Update July 27, 2007)

What is a math trade?

This is a trade between a whole bunch of people at once, using an algorithm (such as used by TradeMaximizer) to decide who should send their game to whom. Because of the algorithm used, you can only get a game you prefer over what you started with. (Or at worst, you may just keep your original game, ie. doesn't trade.)

Sometimes this kind of trade is called a "mathematical no-risk trade list." This is just a longer name for the same thing.

FAQ: in a math trade any potential trades found are always going to be "1 for 1" which is one of your offering(s) that you will ship out (or deliver if it's a "no ship") to another participant in the math trade you will receive exactly one offering (from your "want list" for your offering) from most likely yet another participant. An "offering" is a single geeklist item... however note that the offering/item could be a bundle of more than one thing.

Why is a math trade worthwhile?

By matching together the likes and dislikes of a lot of people at the same time, many more trades become possible. Say person A wants the game Queen's Necklace, and person B has a copy of it which they don't especially want to keep. B doesn't want any of A's games, but would like a copy of Jambo. Person C has Jambo for trade, but doesn't want any of B's games. But C would like Razzia, which person A is interested in trading. So although there's no good trade between two of A, B, and C, the three together can each trade a game away to get a game they really want. The math trade algorithm figures out these fortunate coincidences, and assigns trades so that everyone gets games they want in return for trading away games they don't. In the above example you would have these trades:

A sends Razzia to C, and gets Queen's Necklace from B
B sends Queen's Necklace to A, and gets Jambo from C
C sends Jambo to B, and gets Razzia from A

So you get a circle of trades among the participants.

Like any kind of game trade, this depends mostly on differing tastes. As shown by the many debates here about the "best" games, really each person has different preferences, and it's quite possible for everyone in a trade to be very happy with the outcome. Because of this, math trades are often a great way to get a hard to find game, since one person's old, forgotten game could be your personal treasure.

If you like learning about games, math trades also give you a good reason to find out about a lot of games you might not otherwise have seen. If you just want to trade for games you already know about, though, you can still participate in a math trade without any difficulty -- Just ignore the games you've never heard of.

How does it work?

When someone is willing to moderate a math trade, they start a trade GeekList. In the GeekList, they'll tell you the rules of that particular math trade. Since the rules differ a bit from list to list, you need to read them carefully. Though the rules can differ a little, most parts of a math trade stay the same between lists:

  • The moderator posts a trade GeekList, along with any rules for that math trade.
  • Everyone interested in joining the trading posts the game(s) they'd like to trade as items in the GeekList.
  • At some point (which is usually mentioned in the rules at the start of the GeekList), the math list is closed to new game entries. Usually, the moderator summarizes all of the valid entries in a list, and gives a word or number to name each entry. I'll call these identifying names "IDName" in the example, below.
  • Everyone who submitted a game then figures out which games they'd like from the list. They then send their choices to the moderator, usually using a GeekMail message with a clear subject line. (The moderator is going to be receiving a lot of GeekMail messages, so you want them to have an easy time seeing what your message is about.) The exact format for sending your choices can differ from list to list, but usually goes like

(mybggusername) MyIDName : IDName1 IDName2 IDName3 IDName4

So you list your own game's IDName first, and then follow it with the list of games you'd be willing to trade it for. The games you list are in your order of preference; i.e., the first game you list (after your own) is the one you want the most. If you don't want to trade for a particular game, leave it out of your list. If you don't see any games you want to trade for, you can just send in a list without any wanted games. That is,


  • Once the moderator has everyone's lists of wanted trades, they run the algorithm to find out who should send their game to whom. The most common algorithm has been "maximize trades." I'll describe "maximize trades," below.
  • The moderator posts the list of trades as decided by the algorithm. Some game entries won't be traded at all. But for the rest, you'll be told who to send your game to, and which game you'll be getting in return (and from whom). Unlike with your usual trades, you'll probably be getting your new game from a different person than you'll be sending your old game.
  • Often, the moderator will ask that everyone wait a little while (perhaps overnight) to make sure there weren't any mistakes when running the algorithm.
  • The traders then contact each other. The best way to take care of things is usually with BoardGameGeek's Trade Manager. Just send a trade request to the person you'll be sending a game (and/or to the person who will be sending a game to you). This automatically sends your mailing address, and (most importantly) lets people leave feedback after the trade.
  • Once you know where to send your game, mail it (hopefully fairly quickly) to its recipient. In most math trades, the kind of shipping has been up to the sender. It's best if you keep in contact with the other trader, so they'll know about any delays or problems.
  • Finally, the moderator will post everyone's list of the games they were interested in trading for. This lets all the participants verify that the moderator was honest when coming up with the list of trades.

Differences between math trades

The moderator chooses the rules of the math trade, and if necessary, decides on any problems which come up. Math trades so far have all been pretty similar, but some details have differed. Specifically ...

  • Number of game entries: In some trades, you'll be able to enter 2, 3, or more times. This works just like entering once, but you post multiple game entries and send in a separate list of desired trades for each. (You send all your entries to the moderator in a single GeekMail. And no, you shouldn't list one of your own games as a wanted game for another of your own games.) By sending in different lists for each of your entries, you can be really picky when trading a new copy of Roads & Boats, but decide to accept almost anything in return for your beaten up, incomplete version of Candyland.
  • Deadlines: Some math trades leave lots of time for entries, others are quick. Most automatically end after some number of entries (usually in the range of 100 to 500). Some math trades leave a long time for everyone to turn in their lists of desired trades, while others have a short time. Be very sure to read and consider these deadlines! If you aren't going to have the time to choose between trades, you should wait for another opportunity.
  • Multiple games in one entry: Often, you'll be able to group more than one game together in a single entry for trade. This is sometimes called an "AND," after the conjunction used to describe the offered items. Sometimes you can give the recipient of the entry a choice between games. This is sometimes called an "OR." In most lists, you can add extra games to your entry after the initial listing. These extras are often called "sweeteners."
  • Allowable games: In some lists, the moderator will only allow games which have a specific rating average on BoardGameGeek, or number of people who have listed it as "wanted", or some combination of the two. There have even been lists only for games with less than a certain number of people listing it as "wanted". In a math list with multiple items in the same entry, the limit may apply to all games in the entry, or only to the first game listed. It's likely that moderators will continue to come up with other, new criteria (such as "wargames only") to limit the games for trade.
  • Duplicates: In many lists, duplicate game entries are not allowed, or only one duplicate is allowed of each game. This limit may apply to entries as a whole, each individual game in an entry, or only to the first game listed.
  • Location of traders: Some lists will limit participation to people in the US, or Canada, or some other country or group of countries. Potentially someone could even run a trade for people willing to get together in person in Chicago (for example) as a way to reduce shipping costs. Speaking of which...
  • Shipping costs: This one is particularly important! Most trade lists have the sender pay shipping costs for the items they send. (If the recipient had to pay for shipping, there would be lots of extra Paypal fees or check delays to deal with.) But you should not assume this is the case -- Be sure to read the list's rules to be sure. And it is especially important to check the rules for shipping between different countries. Sometimes there is an assumed country of origin, and anyone outside that country may need to pay the extra shipping. Sometimes extra shipping between countries is explicitly assigned to the sender or the recipient. Sometimes you need to say when you post your entry whether you'll charge extra for shipping outside your country. In any case, be very sure to check these rules, since they may well affect which games you'll be interested in trading for.

What can go wrong?

And how can I avoid any problems?

So you can trade a game you don't want for one you do! That's great, but it's important to know the risks in the "no risk" trade.

  • Be sure to consider shipping and packaging costs when you choose the games you'd like to trade for! Especially if you're trading away a very heavy game, shipping can cost $10 or more. Even if the game you're trading is worthless to you, you shouldn't trade it away for a game worth less than the cost of shipping.
  • Make sure your list of wanted trades is correct! If you list the wrong game entry as one you're willing to trade for, you could get stuck trading for something you don't want! If you made a mistake in your list of wanted games, and ended up with a game you didn't really want, there is at least one trick which can reduce the problem. You may be able to persuade the person who would have sent you the game instead to hold it for you for later trades. You can then trade the game to someone else for something you really want, and have the original owner send it for you.
  • Be careful about addresses! If you accidentally send your game to the wrong person, you'll need to pay to have it sent to the correct address. Similarly, be sure you have your address correct when giving it to the sender!
  • Communicate clearly and quickly! Be sure to give an accurate description of the game you're trading, and contact the people you're trading with if there are any problems which come up. And if you have any question about another person's game entry, do ask them (in the GeekList) for more detail.
  • Be patient! Do not send your game immediately after the trades have been listed by the moderator. Instead, wait about a day for any issues to be raised.
  • Only trade your game in one place at a time! If you offer the same game in two separate trade lists, or have your game listed for sale on BoardGameGeek at the same time you have it in a math list, you can end up obligated to send your game to two people at the same time.
  • "Deadbeat" traders: The worst possible problem in any trade is that the other person just doesn't send their game. In that case, it is important to try to communicate with them, and show some patience -- Many people on BoardGameGeek are very busy with events other than playing games. But it is possible there will be a problem even after trying to communicate. As with other trades, you can (if you used the trade manager) leave appropriate feedback for the trade. If absolutely necessary, you may want to consider listing the trader as "deadbeat." There is a trade GeekList for the listing and discussion of deadbeat traders.

Getting into a math trade

Some math trades fill up very quickly. The best solution for this is usually patience — Eventually you'll be viewing BoardGameGeek at the right time, and be able to post an entry. It's also possible that a moderator could be convinced to announce a math trade in advance, so there would be less incentive to check the trade lists repeatedly.

What is "Maximize Trades?"

Most math trades have used the "maximize trades" algorithm to decide who trades with whom. This algorithm tries to come up with the most trades it can, considering each person's list of wanted trades. When more than one set of trades gives the most total trades, the algorithm favors trades which give people games higher in their priority lists.

If you are interested in a discussion of the algorithm, check here:
Math Trade Theory & Algorithms (Warning: Can Hurt Brain) and (for a big algorithmic improvement) check the last section of the wiki page for TradeMaximizer.
Four implementations of "maximize trades" (along with some variations on it) can be found at:

Tips for new traders

  • Follow the usual guidelines for trades and sales. Describe your game clearly. In particular, mention the condition of the game, if it is in a language other than English, and the edition (if you know). When sending the game, package it carefully.
  • It can pay to check other traders' want lists. By offering a game lots of other people want, you greatly increase the chance you'll get something you want, too.
  • If you're really hoping to get a particular game or games, try to offer a game of roughly the same or higher trade value.
  • When offering multiple items together, try to group games that are related somehow. That way, you're more likely to find someone interested in the whole lot.
  • If you're offering a game which is potentially valuable but has a limited audience (say, an old baseball game), you will probably have better results if you post it early in the trade, so people interested in your entry will be tempted into participating in the math trade.
  • Each person has their own way of choosing what games they're willing to trade for. You can do this intuitively, or with a spreadsheet and lots of numbers. It can be quick if you just choose those games you already know you want, or slow if you read the descriptions of all the games you haven't heard of. In either case, be sure to leave some time for this step!
  • "Tipping" the moderator (giving them a GeekGold) at the end of a math trade is nice but not required (same if you use the OLWLG).
  • If you used the trade manager, be sure to leave appropriate feedback after you receive your game. There is some debate about whether you should leave feedback to the person you sent the game; The most common opinion is that you should generally leave positive feedback to the recipient unless there are serious problems with their communication.
  • For some additional useful ideas, take a look at starspangledgirl's post, here AFTER the Math Trade Guide .

Alternatives to a math trade

Trades on BoardGameGeek have some advantages over sales. There's no fee for the transaction. And everyone involved in the trade gets a game they want (instead of just money). Math trades are nice because they involve so many people in the trading, and often include lots of unusual games.

Ultimate Trades

"Ultimate Trades" are another way of trading between multiple people — They're in some sense a manual version of a math trade, in which people volunteer not only their game, but exactly which game to accept. They give more control to the traders, but give fewer options for trades, and sometimes fail to give any trades at all. For a guide to Ultimate Trades, I recommend a look at Kane's guide at A Guide to Ultimate Trade Lists .

Automated Trade Finders

You can also make use of an automated trade finder on BoardGameGeek which looks for small groups of people with potential trades, as described by grandslam here Automated trade chains! - Just add simple notations . And of course you can just trade directly with another person. That avoids the confusion of the group trades, but only works if you are able to find a very good match with them.

Selling is also an option. It gets you money, which is more flexible (though possibly less immediately enjoyable) than getting a game. But it can involve fees both from Paypal for money transfer and for BoardGameGeek or eBay for the sale. If you use BoardGameGeek a lot, you may want to consider GeekGold auctions for selling low value games — They don't have any extra costs, but you end up with BoardGameGeek funny money for your sale.


If you have any questions about participating in math trades, please post in the trade forums (but preferably not as a response to this post). With a little luck, one of the more experienced traders will have an answer for you.
BGG Trade Forums


Math Trade types discussions

Video Help & Runthroughs

These very useful (but long) videos take you through the entire process very carefully with lots of tips.
Recorded during August 2013 by Rahdo

BGG Video Page:
(I don't know how to link nicely to a BGG video, someone who does please edit!)

YouTube direct links:

Part I (finding a trade and listing your games)

Part II: (building your want list with the OLWLG)

Part III: (shipping your games with the trade manager)

Part IV: (editorial & advanced tips)

Four older (2010) and shorter videos made by boathouselooper are here:

The narrator is not so enthusiastic but the videos are MUCH shorter!

Part 1. Finding Trades and adding items [4m19s]

Part 2: Adding items via the OnLine Want List Generator (OLWLG) [6m24s]

Part 3: Editing your want list in the OLWLG [2m59s]

Part 4: Duplicate Protection in the OLWLG [3m59s]

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