Your Backtest Says +47%. Your Live Account Says -12%. Here's What Happened.

Your Backtest Says +47%. Your Live Account Says -12%. Here's What Happened. You spent two weeks building it. You ran it on three years of hourly data. The backtest said +47% with a 68% win rate. You deployed it. Three weeks later, your live account is down 12%. This is the most common story in algorithmic trading. It has a name: backtest-live divergence . And it's almost never caused by coding bugs or bad data. It's caused by something more fundamental — the market changed regimes, and your strategy didn't know. This post explains why, and how to fix it with regime detection. Not financial advice. Paper trading only. Always validate with paper trading before deploying real capital. The r/algotrading Graveyard If you spend time on r/algotrading, you'll recognize this post archetype: "My strategy backtested beautifully on 2021-2023 data. I went live in January 2026. Down 15% in 6 weeks. I don't understand what happened." The replies are always variations of the same diagnosis: "You curve