A trading day is any day on which you open at least one trade during the market session. It is defined by the official server day, not by your local calendar, and it is used to count profitable days for payouts and to apply the consistency rule.
When does the day roll over?
CFDs and Stocks: the server day starts and ends at the official daily rollover, 21:00 UTC.
Futures: the market session runs from 6:00 PM ET to 5:00 PM ET the next day. A trade opened after the daily rollover counts toward the next session.
What makes a day "profitable"?
A trading day counts as profitable only when it generates net profit of at least 0.25% of the initial account balance. Only closed trades count; floating (open) profits do not count until the position is closed.
Why it matters
Payouts: Futures and Stocks require at least 5 profitable trading days before a payout; on CFDs the requirement varies by challenge.
Consistency: your most profitable day (and, on some products, your most profitable trade) is measured against your total accumulated net profit for the consistency rule.