I have orders in euros and dollars. What happens to them?

The short answer

Orders in a currency other than your store currency are left out of the report and named in a warning above the numbers. No exchange rate is applied.

That is a deliberate refusal, not a missing feature. Summing amounts in three currencies gives a number that looks completely plausible and is wrong by whatever the exchange rates happen to be — and nothing on the screen would tell you.

What WooCommerce actually does

Each order stores its own currency. The cost you enter on a product has no currency of its own — it is implicitly in the store currency. So an order taken in euros carries euro line totals and a cost that was entered in whatever the shop’s base currency is.

Multi-currency plugins handle this in their own ways: some store the base-currency equivalent on the order, some store only the currency actually charged, some keep their own rate table for the day of the sale. There is no core field that says “this order in store currency”, so a report has either to read every plugin’s private convention or to say what it can and cannot do.

What to do about it

• If foreign-currency orders are a rounding error — a handful a year — read the report as it is and note that those sales are excluded.
• If they are a real part of the shop, the honest reading is that this report covers your store-currency sales only. The excluded amount is named, so you know the size of what is missing.
• Do not convert by hand into the same table. Yesterday’s rate applied to last March’s sale is a made-up number, and once it is in the same column as real ones nobody can tell which is which.

How Merchgain reports it

Merchgain detects the currencies present in the period, names them in a warning above the summary cards, and excludes those orders from every figure.

The reason this made it into the first version at all is a lesson learned on our other plugin: a tile once showed an amount roughly sixteen times too low, with no signal that anything was missing. A quiet wrong number is worse than a missing one — so the currencies get named, and the exchange rates stay out.