Your estimate drives the answer
Enter a probability between 0 and 100 percent, excluding the endpoints, and an available fractional or decimal price. The fair decimal price is one divided by the probability. Expected return per unit is probability × decimal price − 1.
Example, not a forecast
With an assumed 25% chance and a 4/1 price, the calculation is 0.25 × 5 − 1 = +0.25 per unit. At 2/1 it becomes −0.25. These outputs are conditional arithmetic. They do not validate your probability, predict a win, or imply that GAMELIN has assessed this race.
Why this calculator never says BET
The actual GAMELIN money decision has field-integrity, exact-data and Conviction requirements in addition to its price tests. A positive number from a probability you typed in cannot bypass those requirements. This tool does not assign a stake, a confidence score or a qualified recommendation.
Try less favorable assumptions
Lower the assumed chance and shorten the price to see how sensitive the result is. The final pari-mutuel price may differ from the price you entered, and your estimate may be wrong. Read overlays and underlays and when to pass before treating a mathematical comparison as evidence.
Fair odds are a break-even boundary
If your estimate is 20%, break-even decimal odds are 5.00, equivalent to 4/1. A longer price produces positive conditional arithmetic; a shorter price produces negative conditional arithmetic. “Conditional” matters: the answer is only as sound as the probability assumption and the price that actually settles.
Run a sensitivity check
| Assumed chance | Fair fractional odds | Expected return at 4/1 |
|---|---|---|
| 15% | About 17/3 | −0.25 per unit |
| 20% | 4/1 | Break-even |
| 25% | 3/1 | +0.25 per unit |
Connect the calculation to a disciplined workflow
Record the source and observation time for the price, test a range rather than one optimistic estimate, and accept PASS when a modest probability change eliminates the apparent advantage. Start with the odds converter for raw implied probability, then compare your assumption here. The Race Lab keeps a real read's probability fixed while testing a hypothetical price. The betting hub connects arithmetic to field verification and responsible limits.
Sources and scope
Official references and GAMELIN's published evidence. Check current track and operator information before acting.