Brier score explained for bettors
The Brier score grades a probability, not a pick. What it measures, how to work it out by hand, and what it says about BAI8's first 79 settled calls.
On this page
A Brier score grades a probability rather than a pick. For every call you take the chance you stated, subtract 1 if it happened or 0 if it did not, square the gap and average the lot. Lower is better: 0 means you were certain and right every time, and saying 50% on everything scores 0.25. On our first 79 settled calls, BAI8 scores 0.234.
Working one out by hand
Take three calls. You said 60% and it won, 40% and it lost, 70% and it lost.
| Stated chance | Happened? | Gap | Gap squared |
|---|---|---|---|
| 60% | Yes (1) | 0.40 | 0.16 |
| 40% | No (0) | 0.40 | 0.16 |
| 70% | No (0) | 0.70 | 0.49 |
| Average | 0.27 |
The third call does most of the damage. Squaring punishes confident misses hard, which is the point: a forecaster who says 90% and misses should pay more than one who said 55%. Glenn Brier introduced the score for weather forecasts in 1950, and it works the same for a match.
Why bettors should care
Win rate rewards picking favourites. A tipster who backs 1.30 shots wins most days and can still lose money. The Brier score does not care about the price; it asks whether 60% calls happen about 60% of the time. That is the half of the job a price comparison cannot check on its own. The other half is the gap to the market, explained in what a positive edge actually means.
BAI8's first 79 calls
| Brier score | |
|---|---|
| BAI8, 79 settled calls | 0.234 |
| Saying 50% on every call | 0.250 |
| Saying the overall hit rate (59.5%) on every call | 0.241 |
And by band, the check a calibration curve draws (see what a calibration curve shows):
| Our stated chance | Calls | Average stated | Won |
|---|---|---|---|
| Under 40% | 18 | 37.9% | 6 (33%) |
| 40–50% | 19 | 45.0% | 14 (74%) |
| 50–60% | 35 | 53.5% | 20 (57%) |
| 60–70% | 6 | 65.6% | 6 (100%) |
| 70% and over | 1 | 78.9% | 1 |
We beat both simple baselines, narrowly. The 40–50% band won far more often than we said, which is either luck in 19 calls or a sign that we were too cautious there. Nineteen calls cannot say which.
What this does not tell you
A Brier score does not tell you whether a bet made money. You can be well calibrated and still find no price worth taking. It also needs volume: on 79 calls a few results swing it by a hundredth either way, and how long you need to wait is the subject of how many bets before a record means anything.
18+. Bet only what you can afford to lose.
Common questions
What is a Brier score in betting?
The average squared gap between the chance you stated and what happened, scored 1 for a win and 0 for a loss. Lower is better; 0 is perfect.
What is a good Brier score?
It depends on the markets, so compare it with a baseline. Saying 50% on every two-way outcome scores 0.25; beating that clearly over many calls is the first test.
What is BAI8's Brier score?
0.234 on the first 79 settled calls, against 0.25 for a flat 50% guess. That is better than the baseline, on a sample still too small to lean on.