Which month does a refund belong to?

The short answer

The month the refund was issued. A sale in September refunded in November leaves September exactly as it was and appears as a negative amount in November.

The alternative — pushing the refund back onto the month of the sale — means a closed month keeps changing behind your back. You would print a September report in October, and get a different September in December.

What WooCommerce actually does

A refund is its own record, attached to the order but with its own creation date and its own lines with negative quantities. When the cost feature is on, those lines get their own negative cost values, so a refund reduces revenue and cost together rather than only the revenue side.

The refund date is the date you clicked the button, which is what makes it usable as a period boundary.

What to do about it

If your accounting treats a refund as a correction to the original period, the two views will differ, and yours is not wrong — it is a different convention. What you can do:

• read the report by the period in which the money actually moved, which is what a bank statement does too;
• export the CSV each month, so you keep a record of what each month looked like when it closed;
• when a refund is large enough to matter, note it against both months rather than arguing with the tool.

How Merchgain reports it

Refunds count as negative amounts in the period they were issued, on every screen and in the export. A month you have already read does not change later — with one exception, which is worth knowing about and is not ours: issuing a refund makes WooCommerce rewrite the recorded cost of the whole original order. That one is explained in a refund changed my historical profit.