Cost per million expresses trading cost as an amount per one million units of notional traded, the convention used in institutional FX. It exists because per-lot commissions, spread markups and percentage fees are not comparable in their native forms, whereas dividing every charge by the notional it applied to puts them all on one axis.
The conversion is worth doing before comparing account types. A per-lot commission is charged against a standard lot of one hundred thousand units, so ten standard lots make up one million; a spread markup converts by taking its money value on the same notional. Once both structures are expressed per million, an all-in spread account and a raw-spread-plus-commission account can be compared honestly at the size actually traded — and the ranking often changes with size, which is precisely what the headline figures conceal.
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Spreads, Commissions and the Real Cost of a Trade
Spread, commission and swap are the three costs on every forex trade — what each one is, when spreads widen, and how to compare pricing fairly.