- Maths reviewed by Josh Miller
- Tested by Diana Westfield
A betting ROI calculator that tells you the number and how much to trust it. 400 bets, £4,000 staked, £4,220 back: £220 profit, a 5.5% yield. Good, right? Maybe. At an average price of 2.50, the honest range on that yield runs from about −6.5% to +17.5%. You could be a long-term winner, or a long-term loser on a hot streak. The free CasinoCalcs calculator shows both the number and that range.
The betting ROI formula
Yield = (total returned − total staked) ÷ total staked ROI on bankroll = profit ÷ starting bankroll
Most people say ROI when they mean yield, and that’s fine: it’s profit per pound staked. ROI on bankroll is different. £220 on a £1,000 bank is 22%, which sounds a lot better than 5.5%, but it depends on how hard you turned the money over. Always compare yields with yields.
Why 400 bets isn’t enough
Each bet at 2.50 is a coin with a big payout. Its result swings by about √1.5 = 1.22 stakes either side of the average. Over 400 bets that averages down to about 6.1% of turnover, and a 95% range is roughly twice that each way: ±12%.
So the calculator’s range runs from about −6.5% to +17.5% here. To pin your yield down to ±2% at those odds you need around 14,000 bets. Odds-on bettors get there faster, longshot bettors much slower.
| Average odds | Bets for ±5% | Bets for ±2% |
|---|---|---|
| 1.80 | about 1,230 | about 7,680 |
| 2.50 | about 2,300 | about 14,400 |
| 4.00 | about 4,610 | about 28,800 |
| 8.00 | about 10,760 | about 67,230 |
What a good yield looks like
Bookmaker margins on big markets run 3 to 6%, so a long-run yield of zero is already beating most people. Over a few thousand bets, 2 to 5% is excellent. Double figures over a few hundred bets is a good run, not a level. If your bets beat the closing price consistently, that’s a better early sign than profit: the CLV calculator measures it.
For a proper significance test, try the luck vs skill calculator. To see how wildly a real edge can swing, run your numbers through the betting variance calculator, and keep the record itself in the bet tracker.
To keep these numbers up to date bet by bet, download the free betting tracker template.
Tracking every bet honestly is one of the best habits in gambling. BeGambleAware.org can help if the numbers worry you.