Fair Odds and Expected Value
Turn a price and a probability estimate into break-even, expected ROI and a sensitivity band — and see when an assumed edge survives uncertainty.
Lab 1 · Fair odds and expected value
Synthetic · deterministicEnter a decimal price and your probability estimate, with an honest range for how wrong it could be.
Break-even probability43.48%
Theoretical EV at estimate+10.4%
EV at range low−3.4%
EV at range high+24.2%
Fair odds of estimate2.083
Probability edge4.52 pts
Full Kelly (estimate)8.00%
Full Kelly (range low)0.00%
No clear advantage. Your range straddles break-even. Whether the bet has value depends on which end of your estimate is right, so there is no clear advantage. A careful analyst treats this as a pass unless better evidence narrows the range.
Show data table
| True probability (%) | Expected ROI |
|---|---|
| 32% | -26% |
| 33% | -24% |
| 34% | -22% |
| 35% | -20% |
| 36% | -17% |
| 37% | -15% |
| 38% | -13% |
| 39% | -10% |
| 40% | -8% |
| 41% | -6% |
| 42% | -3% |
| 43% | -1% |
| 44% | 1% |
| 45% | 3% |
| 46% | 6% |
| 47% | 8% |
| 48% | 10% |
| 49% | 13% |
| 50% | 15% |
| 51% | 17% |
| 52% | 20% |
| 53% | 22% |
| 54% | 24% |
| 55% | 26% |
| 56% | 29% |
| 57% | 31% |
| 58% | 33% |
| 59% | 36% |
| 60% | 38% |
| 61% | 40% |
| 62% | 43% |
| 63% | 45% |
| 64% | 47% |
Educational calculator. Uses only the numbers you enter or seeded synthetic data — no live prices, no staking, no real money.