How accurate are betting simulators?

A betting simulator is accurate when the probabilities it produces match how often things actually happen. If it calls an outcome 30%, that outcome should happen about 30% of the time. That is measurable, on games the model never trained on.

Written by Jesse, NegativeEV. Last updated 7 August 2026.

How do you measure a betting simulator's accuracy?

Score its probabilities against real outcomes, out of sample.

Log loss and Brier score are the standard tests for any probability forecast. Both punish a forecast for being confident and wrong. Calibration is the plain-English version: across every bet a simulator called 30%, close to 30% should have landed.

Out of sample is the part that matters. A model scored on the games it was trained on will look excellent and tell you nothing.

What makes one simulator more accurate than another?

How closely its simulated games reproduce what really happens on the field.

That is the whole job: the fat tail of a blowout inning, the rate a specific hitter goes deep, the way a game breaks open late. Accuracy is earned there. It is not earned by copying a number off a screen.

How does NegativeEV measure itself?

Continuously, against real outcomes.

Every model in the chain is scored against what actually happened. When the simulator forecasts something worse than the market does, that is treated as a flaw to fix upstream in the data or the models. It is never patched over at the betting layer.

That discipline was learned the hard way: how the simulator was built tells the story, including the backtest that data leakage ruined.

What can a betting simulator not promise?

A guaranteed edge over a sharp sportsbook. Anyone promising that is telling you something about themselves.

The narrower claim is the checkable one. Building a probability from a faithful simulation of the game is a different method than shopping lines, and it is the only method that can be more accurate than the market rather than, at best, as accurate as it. A bet that cannot be matched to a simulated game comes back ungraded rather than guessed at.

Any bet can be pasted in and the simulated probability read directly. Ten free checks a day, unlimited when signed in.

Background: how sim-grading works.