Commission per side versus round turn in the tester

[Amanhasnoname]

Testers ask for commission settings, and misinterpreting them changes results by a factor of two. Some platforms and brokers quote commission per side, others per round turn. A tester configured with the wrong convention either doubles or halves the cost.

For scalpers, where costs are a large share of profit, the mistake alters the conclusion. A strategy that looks marginally profitable with half the true cost may be unprofitable in reality.

Verify the convention by comparing the tester's reported commission on a sample trade with the actual charge on a live trade of the same size. Check both the open and the close for charges.

Also check whether commission scales with lot size linearly, whether there is a minimum, and whether the currency of the charge matches the account currency.

In custom backtesting frameworks, the cost model is under the developer's control, and tests should confirm the numbers against real statements.

The easiest way to avoid errors is to reconcile a handful of live trades against the cost model before trusting any backtest.

How was the commission setting in the tester verified against live charges?