This betting variance calculator shows how far luck can swing your results. It simulates 40 bettors who all place the same bets at the same odds with the same edge, then charts how differently they finish.
Think of it as a reality check: even with a genuine edge, not every one of those bettors ends up ahead.
Variance simulator
Key points
- Every run is random, so the 40 results change each time.
- Expected profit = number of bets × stake × edge.
- The bigger the odds, the wider the swings.
Using the calculator
Enter the number of bets, the decimal odds, your edge as a percentage and your stake, and the calculator plays out 40 bettors.
It charts every path and shows the expected profit, the middle result, the lowest and the highest. It also counts how many finished ahead and gives the typical longest run without a winner.
Worked example
Worked example
Suppose you place 800 bets of £5 at 2.50 with a 4% edge. Each bet then lands 41.6% of the time, because 1.04 ÷ 2.50 = 0.416.
The expected profit is 800 × £5 × 4% = £160, but the standard deviation over 800 bets is about £174, so results spread out a long way.
Roughly four bettors in five should finish ahead, about 33 of the 40, and a longest run of around 11 bets without a winner is typical. Your own run will differ, because every simulation is random.
Reading the results
A few hundred bets isn’t enough to prove an edge or to rule one out. A poor month doesn’t mean your method is broken, and a good month doesn’t prove it works. Our betting variance guide explains how many bets you really need.
The calculator also assumes your edge is real. If it isn’t, the middle result drops below zero, so treat any edge as unproven until your records show otherwise.
Why it matters for staking
Swings like these are why stakes should stay small compared with your bankroll. The Kelly calculator sizes stakes to your edge, and the betting ROI calculator shows how your own record compares. For the maths of win counts, see the binomial distribution.
Related guides and calculators
18+ only. Betting should stay fun. Set a budget before you start, only bet what you can comfortably afford, and take a break whenever you need one. For free, confidential support, visit BeGambleAware.org or call the National Gambling Helpline on 0808 8020 133.