Flash P\&L Versus Final P\&L

Right after markets close, a trader wants to know how the day went, so the desk produces a flash P&L — a quick estimate built from whatever prices and fills were available in the first few minutes, often using approximate closing marks and not-yet-reconciled trade records. Hours later, once operations has matched every trade against the broker's records, applied official closing prices, and booked any corporate actions or fee adjustments, the final P&L is published. The two numbers can differ by a meaningful amount, and the gap between them is completely normal rather than a sign of an error.

The differences usually come from a small number of sources: a handful of trades that hadn't settled into the system yet when flash ran, a closing price snapshot that gets replaced by the exchange's official settlement price, or a fee or borrow cost that only gets calculated overnight. None of these are mistakes in the flash number — flash is explicitly a fast estimate, not a promise.

Worked example

A desk's flash P&L shows +$180,000 at 4:05pm using a preliminary close. By 9pm, final P&L shows +$165,000: two large trades hadn't been captured in the flash feed (net -$10,000 impact) and the official settlement prices for two positions came in slightly different from the flash snapshot (-$5,000). The $15,000 gap is fully explained and reconciled — a trader who only ever saw flash and assumed it was final would be surprised, but nothing was actually wrong.