Spent 3 months building an algo. Took 1 week live to realize I was trading my backtest, not the market.
u/Thiru_7223 ·
Reddit — r/algotrading
· April 01, 2026 at 11:21
· ⬆ 16 pts
· 💬 17 comments
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AI Summary
Summary
Author describes a trend-following algorithmic strategy that performed well in backtests but failed in live trading due to a mismatch in market volatility regimes.
Thesis: A common pitfall in algo trading is overfitting to a specific market regime during backtesting; "enough data" is not the same as "representatively diverse data."
Quality assessment: Personal anecdote and cautionary insight, not well-researched DD. It's a reflective post on a common quant mistake.
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Been running a trend-following strategy I built over 3 months. Logic felt clean, OOS looked decent.First two weeks live it held up. Week three it started bleeding. Nothing dramatic just consistent small losses where I expected small wins.Turned out my strategy was optimized for one volatility regime. The backtest period happened to be unusually stable. Live wasn't.I assumed "enough data" meant "representative data." Not the same thing.
Did anyone else catch this the hard way? Is there a clean way to check for regime mismatch before going live?