About this game
This game lets you try the "prediction market" format, known from services such as Polymarket, using only numbers inside this screen. It is not affiliated with Polymarket.
What you cannot do
- The "yen" you use in this game is not real money. It is only a number inside this screen and has no value.
- It cannot be bought, sold, cashed out, exchanged for prizes or points, or given to anyone.
- Even if you are correct, you receive nothing. Only the number on the screen goes up.
- There is no ranking and no view of other people's results. There is no function to forecast automatically in a row.
- It is not connected to the numbers in our other games (rock-paper-scissors, three-in-a-row, demo trading).
- This is not investment advice. Questions about prices are not recommendations to buy or sell currencies, bonds or anything else.
- This game imitates trading on forecasts with money. If you are under 18, please read this with a parent or guardian. This game does not check your age.
How to play
- The starting balance is 100,000 yen (a record is created the first time you use some on a forecast).
- Choose a question, enter an amount and press Yes or No to buy shares on that side. Each share on the correct side adds 1 yen to your balance; shares on the wrong side add 0.
- The cheaper a side is, the more shares the same amount buys (for example, using 100,000 yen on a side priced 0.1 adds roughly 8 times that if correct, and 0 if wrong).
- After the closing time you cannot buy. Shares cannot be given up early.
- "Start over" sets your balance back to the start (your shares and history are erased).
How prices work
- A price is a number between 0 and 1; Yes and No add up to 1. It moves only with the amounts bought, by a fixed formula (automatic pricing, a logarithmic rule known as LMSR). You can buy even when nobody else is here.
- Formula: cost of k shares = b × ln(1 + p × (e^(k÷b) − 1)), where p is the current price of that side and b is how hard the price is to move (2,000,000 in this game).
- The number of shares is rounded down and the amount deducted is rounded up (never more than you entered). You can use from 100 yen up to your balance at a time. Purchases that would push the price above 0.99 are not accepted.
- A price does not show how likely an answer is and is not a weather forecast. The starting price is either a ratio counted from past published figures or, where we have not counted, 0.5; it is not our view (stated for each question). For weather forecasts and warnings, please see the Japan Meteorological Agency's announcements.
How answers are decided
- Answers are decided by published figures. There are no questions decided by our opinion. Which organisation, which page and which figure is stated for each question from the start.
- We do not make questions about people's misfortune (damage, accidents, illness, war and so on), about election or court outcomes, or about the reputation of people or companies.
When a question is made void, and later corrections
- If the figure has not appeared at the source 7 days after the decision date, the question is made void and the amount used on it is returned as it was.
- It is also made void if the source gives no figure (for example, missing data) or the page no longer exists.
- We decide the answer after opening the source page twice and seeing the same figure. If the source later corrects the figure (for example, a revision of a preliminary value), the decided answer does not change. The figure we saw and the times are kept under "Finished questions and results".
- If we find a mistake of ours in the wording or the rule, the question is made void.
- If the answer becomes known before the closing time, we may close the question early.
Source organisations
We read figures published by the Japan Meteorological Agency, the Bank of Japan, the Ministry of Finance and the Statistics Bureau of Japan in order to decide answers. This game is not made or endorsed by any of them.
What is stored
- From the first time you use some on a forecast, one random number is stored in a cookie (180 days). Nothing is stored just by opening the pages.
- On our server, your balance, shares and history are stored against a value derived from that number. We do not collect your name or e-mail address. IP addresses and browser names are not put in this record.
- "Start over" erases your shares and history. Records with no activity for 180 days are deleted. We also count totals not linked to any person (pages opened, forecasts made, amounts per question, start-overs).
Who made this
The screens, text, questions and calculations were made by AI (Claude) and are published by Microfund Inc. It has not been checked on a real smartphone. The English and Chinese text has not been read by native speakers.