Odds & Implied Probability Converter
Sportsbook odds and prediction-market prices are the same probability dressed up differently. This tool converts between American, decimal, fractional odds, implied probability and prediction-market cents instantly — type into any field and the rest update. Use it to spot when a sportsbook line and a prediction market disagree on the same outcome.
How the conversions work
Every odds format is just implied probability in a different costume. The conversions are exact — no rounding losses except for fractional odds, which are approximated to the nearest tidy fraction.
From implied probability (the universal form)
- Decimal odds = 1 / probability. So 50% probability → 1 / 0.50 = 2.00 decimal.
- American odds (favourite, prob ≥ 50%) = -100 × probability / (1 - probability). So 60% → -150.
- American odds (underdog, prob < 50%) = 100 × (1 - probability) / probability. So 40% → +150.
- Prediction market cents = probability × 100. So 40% → $0.40 YES contract.
Why this matters for prediction markets
Most beginners coming to prediction markets from sportsbooks default to thinking in American or decimal odds. Prediction markets price in cents — a YES contract at $0.40 is a bet that pays $1 if the event happens, costing $0.40 now. That's the same as American odds of +150 or decimal odds of 2.50.
The faster you can read prediction-market prices directly as probabilities, the better — but until then, this converter lets you compare a Roobet or Polymarket price to a sportsbook line on the same outcome in seconds.
Common conversions
| Probability | Decimal | American | Fractional | PM Price |
|---|---|---|---|---|
| 10% | 10.00 | +900 | 9/1 | $0.10 |
| 25% | 4.00 | +300 | 3/1 | $0.25 |
| 33% | 3.00 | +200 | 2/1 | $0.33 |
| 40% | 2.50 | +150 | 3/2 | $0.40 |
| 50% | 2.00 | +100 / -100 | Even | $0.50 |
| 60% | 1.67 | -150 | 2/3 | $0.60 |
| 67% | 1.50 | -200 | 1/2 | $0.67 |
| 75% | 1.33 | -300 | 1/3 | $0.75 |
| 80% | 1.25 | -400 | 1/4 | $0.80 |
| 90% | 1.11 | -900 | 1/9 | $0.90 |
| 95% | 1.05 | -1900 | 1/19 | $0.95 |
How to spot prediction market vs sportsbook arb
Use the converter as a probability translator. If a sportsbook is offering a player to win MVP at +250 (28.6% implied) and a prediction market has the same outcome at $0.35 (35% implied), the prediction market price is higher than the sportsbook price. One of them is wrong — either the prediction market is overrating the player, or the sportsbook is underrating them.
For non-arb users, the more durable use is just sense-checking. Before sizing a bet on either venue, paste both prices into the converter and ask yourself which probability you actually believe. The cheaper venue (lower implied probability for the side you want) is the better fill — assuming liquidity is there.
Related tools and guides
- How Prediction Markets Work — full beginner's guide to YES/NO contracts, implied probability and resolution
- Prediction Markets vs Sportsbook — when to use which, and how to combine them
- Bankroll Survival Calculator — sizing logic for any negative-EV game
- Roobet Prediction Markets Review — full breakdown of the Roobet PM product
- Roobet vs Polymarket — comparison of the two crypto-native prediction markets
- Best Polymarket Alternatives 2026 — full ranking
