How accurate are the Grand Slam of Darts odds?
The closing prices of 244 finished games since Sat 13 Nov 2021, set against what happened: the chance the market gave, with the bookmakers' margin removed, next to how often it came in. A record of what the market did, not a tip.
The market's record
244 games, 2 bookmakers- Closing favourite won 68% 165 of 244 games
- Market Brier score 0.398 0 is perfect; a coin flip scores 0.500
- Average closing payout 95.8% 100% minus the bookmakers' margin
- Games covered 244 Sat 13 Nov 2021 to Sun 16 Nov 2025
37 of the 281 games finished in that time are left out: no bookmaker had a closing price on every outcome.
Market chance against what happened
| Market chance | Price | Selections | Market said | Happened | Diff |
|---|---|---|---|---|---|
| 10-20% | 5.00 to 10.00 | 40 | 15.0% | 12.5% | -2.5 pts |
| 20-30% | 3.33 to 5.00 | 57 | 25.5% | 29.8% | +4.3 pts |
| 30-40% | 2.50 to 3.33 | 63 | 35.6% | 41.3% | +5.7 pts |
| 40-50% | 2.00 to 2.50 | 60 | 45.3% | 48.3% | +3.0 pts |
| 50-60% | 1.67 to 2.00 | 70 | 54.1% | 51.4% | -2.7 pts |
| 60-70% | 1.43 to 1.67 | 63 | 64.4% | 58.7% | -5.7 pts |
| 70-80% | 1.25 to 1.43 | 57 | 74.5% | 70.2% | -4.3 pts |
| 80-90% | 1.11 to 1.25 | 40 | 85.0% | 87.5% | +2.5 pts |
Every priced outcome of every game is one selection. "Market said" is the bookmakers' average implied probability with the margin removed; "Happened" is how often that outcome came in. On the diagonal the market was right on average; above it, that kind of result happened more often than the prices said. Bands with fewer than 30 selections are left out.
Home, away
| Outcome | Market said | Happened | Diff |
|---|---|---|---|
| Home win | 62.2% | 63.5% | +1.3 pts |
| Away win | 37.8% | 36.5% | -1.3 pts |
The market's average closing chance for each outcome over all 244 games against the share of games it won. "Home" is the first-named side.
Bookmaker accuracy
lower is better| Bookmaker | Games | Brier score | vs market average | Payout |
|---|---|---|---|---|
 Unibet |
202 | 0.386 | +0.002 | 95.8% |
 Bet365 |
178 | 0.399 | +0.004 | 95.0% |
Each bookmaker's own closing prices, margin removed, scored against the results of the games it priced; "vs market average" compares it with the bookmakers' average on the same games, so a negative figure means its prices were the closer. Bookmakers with fewer than 50 priced games are left out. Differences of a few thousandths are noise; a much higher score usually means the bookmaker's last price was captured well before the start, so it is the price in our archive being scored, not the trader.
Odds accuracy FAQ
How accurate are Grand Slam of Darts odds?
What is a Brier score?
Does a well-calibrated market mean the odds cannot be beaten?
See the league's fixtures, results and the favourites' recent record on the Grand Slam of Darts page, every game behind these figures in the Grand Slam of Darts results and closing odds by season, or work out a price's implied chance and closing line value with the betting calculators.