ASTRA QUANTPrediction market probability calculator
Enter a contract price and a stake. The calculator shows the implied probability, how many shares you get, what you receive if the outcome wins and your profit. It is fee-free: real trades can include spread or fees, so treat the result as the clean baseline.
Updated: 1 November 2026. Educational material, not financial advice. Astra Quant is independent and not the official Polymarket site.
Calculator
Fee-free calculation. Spread and fees are not included.
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How the calculator works
A prediction market contract pays $1 (100¢) if the outcome happens and $0 if it does not. Everything else follows from that single fact:
- Implied probability = price in cents ÷ 100. A price of 35¢ means about 35%.
- Shares = stake ÷ price. $20 at 35¢ buys about 57.14 shares.
- Payout if it wins = shares × $1 = $57.14.
- Profit if it wins = payout − stake = $37.14, or about 186% of the stake.
- If it loses the shares are worth $0 and you lose the stake.
The stake can be in any unit — dollars, ASC or demo ASCD tokens — the ratios are the same.
Worked examples
| Price | Probability | Stake | Payout if wins | Profit |
|---|---|---|---|---|
| 10¢ | 10% | 10 | 100.00 | 90.00 |
| 25¢ | 25% | 10 | 40.00 | 30.00 |
| 50¢ | 50% | 10 | 20.00 | 10.00 |
| 75¢ | 75% | 10 | 13.33 | 3.33 |
| 90¢ | 90% | 10 | 11.11 | 1.11 |
The pattern is the key lesson: cheap contracts pay a lot when they win but win rarely; expensive contracts win often but pay little. Neither is “better” — what matters is whether the price is below or above your own estimate of the chance.
Using it to find value
Suppose a market prices Yes at 35¢ and, after reading the rules and the news, you believe the chance is closer to 45%. Your expected value per share is 0.45 × $1 − $0.35 = +$0.10. If you believe the chance is 25%, the expected value is 0.25 − 0.35 = −$0.10, and buying No might be the view that fits you. The calculator gives you the market’s number; your edge, if any, is the gap between that number and your own estimate.
What the calculator does not include
- Spread. You buy at the ask and sell at the bid. In a thin market that gap can be several cents. Check the bid/ask on the market page and use the price you would actually pay.
- Fees. The calculator is fee-free by design. If a platform charges a fee, subtract it from the payout yourself.
- Selling early. If you sell before resolution, your result depends on the price at that moment, not on the $1 payout.
Converting to betting odds
Decimal odds are 1 ÷ price: 35¢ → 2.86, 50¢ → 2.00, 80¢ → 1.25. If you compare with a bookmaker, remember that the bookmaker’s odds include its margin, while a prediction market price includes a spread. Why the two differ is explained in How prediction market odds work.
Try it on a real market
The live example on this page loads a current market from Astra Quant and fills its Yes price into the calculator automatically. Change the stake to see the payout, then open the market to see its chart, volume and rules. If you are new, register to get 1000 ASCD demo tokens (virtual, no monetary value) and place a practice trade. More background: What is a prediction market, How to read a Yes/No market, and the longer article How a contract price becomes a probability (Russian).
Frequently asked questions
How do I calculate the probability from a prediction market price?
Divide the price in cents by 100. A contract at 35¢ implies about a 35% probability.
How much do I win on a prediction market?
Each winning share pays $1. Your payout is stake ÷ price; your profit is payout minus stake. $10 at 25¢ pays $40, a $30 profit.
Does the calculator include fees?
No, it is fee-free. Subtract any spread or fee yourself to see the net result.
What happens if my outcome loses?
The shares settle at $0 and you lose the stake.
New accounts receive 1000 ASCD demo tokens — virtual, with no monetary value.