9/21 EMA Crossover — Disproof verdict

The beginner trend system — "buy when the fast EMA crosses the slow EMA, sell when it crosses back." Sold as a complete mechanical system requiring no discretion.

Verdict: dead — grade D, 0 of 2 markets survived, tested on BTCUSDT from 2023-05-16 to 2026-08-30.

At zero cost: +193.0%
With real costs (15bps + 2bps slippage): +170.1%
Out-of-sample: +3.9%
Buy and hold over the same window: +190.9% (the strategy is 20.8 points behind buy and hold)

Rules tested

strategy "9/21 EMA Crossover"  (long)
indicators:
  fast = ema(9)
  slow = ema(21)

entry: when fast crosses above slow
exit:  when fast crosses below slow
# fills next open · fees+slippage on · 70/30 OOS · deflated-Sharpe gate

How this was reconstructed

Literal: long when EMA(9) crosses above EMA(21), flat when it crosses back below. No filter, no stop — exactly the rule as taught. Decisions are taken at bar close and filled at the next open.