Two Thirds: a daily guessing game where the answer is everyone else

01  What it is

Two Thirds is a free browser edition of the "guess two-thirds of the average" game, also known as the beauty contest. Economists have used it for decades to measure how many steps ahead people think about what other people are thinking. The rule fits in one sentence. Everyone picks a whole number from 0 to 100. The target is two-thirds of the average of all the picks. Whoever picked closest to the target wins, and if several numbers are equally close, they all win.

Most daily web games give everyone the same puzzle and score it against an answer that was fixed in advance. This one has no answer until the day ends, because the answer is built from the picks. Your own number moves it. A day runs from midnight to midnight UTC, so it is the same day for everyone in the world. Everyone who plays that day is one crowd, and you are playing against all of them.

You get one pick a day, and you cannot change it. There is no account, no sign-up and no email. There is also no prize: a win is bragging rights and nothing else.

02  What happens when you lock in

The page is a number pad, a "Lock in" button and a line saying how many people have locked in today. That count is the only thing you can see about today’s crowd. The picks themselves stay hidden until the day closes, because seeing them would change them. If everyone could watch the average forming, the game would become a race to read the screen.

As soon as you lock in, the game gives you a thinking level: a short label for the reasoning your number suggests. The labels follow the classic chain of the game. A level 1 player assumes everyone else picks at random, which puts the average near 50 and the target near 33. A level 2 player assumes everyone else is level 1 and aims near 22. A level 3 player undercuts the 22s, and so on, down towards zero. The bands in the app are fixed:

• 41–67 is Level 0: you picked freely. 28–40 is Level 1, 19–27 is Level 2, 13–18 is Level 3, and 2–12 is Level 4+.
• 0 is the Nash purist. It is the textbook equilibrium, and the label points out that it almost never wins against real people. 1 is "Level ∞, with a hedge".
• 68–99 is the wildcard. The target can never be higher than 66.7, because even a crowd of nothing but 100s averages 100. Exactly 100 is the saboteur.
• 42 and 69 are the comedian.

03  The reveal, and the card it makes

At midnight UTC the day closes and its full histogram is published: how many people picked each number from 0 to 100. Every pick is counted the moment it is made and stored with the day it was made, so a closed day can never be changed afterwards. Come back after midnight and the page shows the previous day as a card. It has a dashed line at the target, the winning bar in its own colour, your own pick marked underneath in amber, and labels on the biggest spikes. If 0 or 100 got at least 3% of the picks, they are labelled too.

Under the card you get the exact numbers: the target to one decimal place, the average, the number of players and the winning pick or picks. If you played that day, you also see how many of the other players you were closer than. Your own pick is left out of that comparison, so you are never counted as beating yourself.

The card is a 1080×1350 image made for sharing. On phones that support it, "Share the card" attaches the image itself. Elsewhere it copies a line of text and a link. The link opens that exact day’s reveal rather than whatever is newest. "Save image" downloads the card as a PNG. Before the reveal, you can still dare a friend. That message names your thinking level, not your number. For the labels that stand for exactly one number (0, 1, 42, 69 and 100), even the level is left out, so the message never gives your pick away.

A row of past days sits under the reveal. Each one shows its target and how many people played, going back up to 30 days, so you can watch whether the crowd’s target drifts as regular players learn. Days nobody played are skipped.

04  Honest about small crowds and stuffed ballots

A crowd game is only as good as its crowd, and Two Thirds does not hide how big the crowd is. Every card prints the player count. Below 20 players, the card says "small crowd today" and draws the bars on a fixed scale, so seven picks do not look like seven thousand. The target is still worked out exactly. Day 1 was 2 October 2026, so the archive is young. Until the first day closes, the reveal panel says when it will arrive. It also gives one real number for scale: when the Danish newspaper Politiken ran the game in 2005, 19,196 readers took part and the winning number was 21.6.

The rules against ballot-stuffing are modest, and the game says so. Your browser remembers that you have played today. On the server, each network address can lock in at most five picks a day. That limit is not one because offices, campuses and mobile networks put many people behind a single address. The address is never stored as it is. It is scrambled together with a random value that changes every day, and that day’s value is deleted after two days, after which nothing can be traced back to an address. Picks from automated test browsers go through the full flow but are not added to the tally, and the page tells you so.

05  How to approach your first pick

The game is easy to understand and hard to win, because the right answer depends on who turned up. A few things are worth knowing before you play:

• Never pick above 67. It cannot win, whatever anyone else does.
• Zero is not a trick answer. It is where perfect logic ends up, but you win only if nearly everyone else reasons all the way down too, and real crowds have not.
• In the big published editions, the winning number has usually landed somewhere between the low teens and the low twenties. Treat that as a starting point, not a rule.
• Think about where today’s players came from. A crowd sent by an economics forum reasons further than one that arrived from a group chat.
• A few protest 100s pull the average up more than you would expect, and the card labels them when there are enough of them to matter.

06  Questions people ask

Where can I play the guess two-thirds of the average game online?

Two Thirds runs it every day in the browser, free and without an account. Pick a number from 0 to 100, lock it in, and come back after midnight UTC to see where the whole crowd landed.

What number wins the 2/3 of the average game?

No number wins every time. It depends on what everyone else picks. Perfect reasoning leads to 0, but real crowds stop well short of it. In Politiken’s 2005 edition, with 19,196 players, the winning value was 21.6. Anything above 67 can never win.

Why can’t I see today’s results?

Because they would change today’s picks. Only closed days are published. While a day is open, the page shows only how many people have locked in. The full histogram appears at midnight UTC.

Can I change my number after locking in?

No. You get one pick per UTC day and it is final. A new day, with a new crowd, opens at midnight UTC.

Is there a prize for winning?

No. There is no entry fee and no prize. Winning shows on your reveal card and nowhere else.

What happens if two people pick the same winning number?

They both win. Every pick at the smallest distance from the target is a winner, including two different numbers the same distance away on either side, and the card says how many players landed closest.

07  More from the shelf

• Same Storm — Two crowds. Two ships. One storm.
• BracketDay — Tap the bracket. Crown your champion.
• HoldOut — How long can you hold it?
• Isobath — Drop a pin. Find out how wrong you were.

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