Demo versus live on the same EA: what to compare and why they differ

[FXS London Scalper]

Running the same EA on demo and live with identical settings is the cheapest way to see what live trading costs you. The metrics to put side by side: trade count, win rate, profit factor, and average slippage on entries and stops.

A hypothetical EURJPY example of what the gap can look like:

• Demo: 218 trades, 61% win rate, profit factor 1.38, no slippage.
• Live: 204 trades, 57% win rate, profit factor 1.12, slippage −0.3 pips on stops and −0.1 on entries.

Where differences like that come from:

1. Trade count. A spread filter can block signals live that pass on demo, if demo spreads are tighter, which is common in Tokyo hours.
2. Fills. Demo often fills at the exact price. Live doesn't.
3. Partial closes. A partial close can fail live because of minimum volume.

In that example, demo overstates profit factor by about 0.26. Anyone scaling up on demo results would be disappointed.

A practical rule follows: require a demo profit factor comfortably above your minimum, by a margin you've measured on your own pair of accounts, because live will pull it down.

Has anyone measured the demo-live gap on their EAs? I'd like to know what margin is typical.