A good horse is not always a good price.

Overlay and underlay

An overlay is a price more generous than your estimated fair price. An underlay is a price shorter than your estimate supports. Both depend on the quality of that estimate. Calling a horse an overlay does not make the underlying probability correct.

Work from a probability assumption

At an assumed 25% chance, break-even decimal odds are 1 / 0.25 = 4.00, equivalent to 3/1. At 4/1, a one-unit winning bet returns five units. The simple expected return is 0.25 × 5 − 1 = +0.25 per unit. At 2/1 it becomes 0.25 × 3 − 1 = −0.25. These are illustrative assumptions, not forecasts or a guaranteed result.

Market edge is not the same calculation

A model probability can exceed the runner's normalized share of the market while the actual displayed price still fails the monetary test. Normalizing the whole field changes the comparison baseline; it does not change what a winning ticket pays. GAMELIN therefore distinguishes probability-point edge from price expected value.

Why the simple calculation is not a BET signal

An estimated positive return can disappear if the probability is inaccurate or the final price shortens. GAMELIN's full decision also depends on exact input coverage, field integrity and Conviction. A manual probability typed into a calculator does not pass those checks.

Check sensitivity instead of chasing a label

In the fair-odds calculator, lower your assumed probability and try a shorter price. If a small change reverses the arithmetic, the apparent advantage is fragile. Do not enlarge a stake to compensate for uncertainty. PASS remains a complete decision.