how many backtested trades before you actually trust a system live
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ive got a system showing a positive expectancy over about forty backtested trades and im itching to go live. but forty feels thin and im worried im fooling myself with a small sample. whats a sample size you personally consider enough to trust a system with real money, and does it depend on the strategy type?
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forty trades is far too few to trust, youre right to be suspicious. forty trades can show a strong positive expectancy purely by luck. i want at least a few hundred trades across multiple market regimes before i believe a system, and even then i go live small. the lower your win rate and the higher your variance, the more trades you need to separate edge from luck. forty is a hint, not evidence.
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it absolutely depends on the strategy. a high-frequency system generating thousands of trades reaches statistical significance fast. a swing system taking a few trades a week might need years of history to accumulate a few hundred trades, which is why swing systems are genuinely harder to validate. match your required sample to your variance, but forty is below the threshold for basically any style.
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the people who go live on forty trades and win for a while are the most dangerous, because the small-sample luck convinces them theyre geniuses right before the real distribution shows up and humbles them. a tiny winning sample is worse than a losing one, it funds overconfidence.
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the troll describes a real trap, early small-sample success breeding overconfidence and oversizing right before reversion. the protection is to size as if the edge might be illusory until the sample is large, so even if forty trades was luck, going live tiny means the lesson is cheap rather than account-ending. treat early live trading as continued testing with real money, not as confirmation youve arrived. let the sample grow before the size does.
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