How long a losing run can honestly last
Most people's sense of a normal bad run is far too short. Here are the actual numbers, and what they mean for reading your own record.
Ask somebody with a 50% method how many losses in a row would worry them and most say five or six. The honest answer, over a year of betting, is somewhere past twelve.
The numbers
At a 50% strike rate, the probability of any given run of ten starting at a particular bet is roughly one in a thousand. That sounds reassuring until you count how many starting points a year contains. Over 500 bets there are hundreds of places such a run could begin, and the probability of at least one appearing somewhere is better than even.
Drop the strike rate to 40%, which is entirely normal for somebody backing
prices around 2.60, and runs of fifteen become unremarkable.
Why this is the most useful thing in bankroll management
Almost every account that ends at zero does so because the stake was sized for a bad run that was shorter than the one that arrived. The method was often fine. The estimate of what a bad run looks like was not.
So the practical question is never "am I confident in this edge". It is "what happens to this bankroll after fourteen consecutive losses", and if the answer is that there is nothing left, the stake is wrong regardless of how good the method is. That is the whole argument of staking without going broke, reduced to one number.
What it means for reading a record
A run tells you almost nothing about a method, because runs of that length happen to good methods routinely. What it does tell you is whether you can survive the next one, and that is a question about the stake and not about the selections.
What this does not tell you
These numbers assume bets are independent, and they are not. Somebody who follows one league is exposed to the same weather and the same referee tendencies across a weekend, so their losses arrive in clumps that are worse than the independent case. The honest figures are therefore a floor.
Common questions
How long can a losing run last with a winning method?
Longer than intuition suggests. A method winning half its bets will produce a run of ten losses somewhere in a year of five hundred bets more often than not.
Does a long losing run mean the edge is gone?
Not by itself. Distinguishing a broken method from ordinary variance takes a much larger sample than a single run, which is why single runs are poor evidence.
How should a losing run change what I do?
It should change the stake before it changes the method, and it should change neither on the basis of the run alone.