Where Did Today's P&L Come From?

Knowing the book made $180,000 today tells you almost nothing about whether to trust it. Attribution is the step most traders skip under time pressure and regret skipping the one day it mattered: tracing the number down to which positions, which price moves, and which of your own decisions produced it.

Working from the top down

Start at the book level and split by strategy or sub-book, then within a strategy split by name, then within a name split by cause. At each level you're asking the same question — does this piece look like what I'd expect, given what I know happened today?

A book-level $180,000 gain might be $220,000 from the equity long/short sleeve and a $40,000 loss from the pairs sleeve. That alone is useful: it tells you the sleeves are not moving together today, which is either healthy diversification or a sign one sleeve is picking up risk the other is losing. Drilling into the equity sleeve, you find three names drove almost all of it — two beat earnings, one got no news at all and simply drifted up with the sector. The third one is the interesting case: no obvious catalyst means either the position is bigger than you remembered, or something is happening you haven't seen yet.

Separate price-driven from position-driven

The same dollar of P&L can come from two very different places: the market moved and you were positioned for it, or your position size itself changed (you added, you trimmed, a corporate action changed your share count). Conflating the two is a common error — a position that "made money" partly because you doubled it mid-morning did not perform twice as well; it performed the same and you took twice the risk.

A worked attribution

The book is up $180,000. Attribution walk:

• Equity long/short: +$220,000. Of that, +$140,000 from a single name (ACME) that beat earnings and gapped up 6 percent — expected, the position was sized for exactly this kind of move. +$80,000 spread across eleven other names, each a normal drift, nothing to flag.
• Pairs sleeve: -$40,000. The long leg was flat; the short leg rallied 4 percent on a sector rumor with no fundamental read-through. This is basis risk showing up, not a broken thesis — worth a note, not a reaction.

Every dollar has a home. Nothing is left in an "unexplained" bucket, which is the actual goal of the exercise — not to celebrate or worry about $180,000, but to confirm that the pieces which make up $180,000 are each individually sensible.

Bottom-up as a cross-check

Top-down attribution — book, then sleeve, then name — is the fast pass, but it's worth occasionally running the check the other way: pick a handful of the largest individual positions and ask what each one did today, independent of the total. This catches a specific failure mode the top-down pass can miss, where two large offsetting moves net out to something small and unremarkable at the sleeve level while each individually was a much bigger event than the summary line suggests. A position up $300,000 and another down $280,000 nets to $20,000, which looks like a quiet day in the top-down view — but a $300,000 single-day move in one name is exactly the kind of thing worth understanding on its own, whether or not the desk-level total happens to be unremarkable.

Building the habit

The point of doing this daily, even on quiet days, is that attribution gets much harder to do well once several days have compounded. A position change from three sessions ago is a fuzzy memory; a position change from this morning is still on the blotter. Desks that skip attribution on "boring" days are the ones that struggle most when a genuinely bad day arrives and they have no recent baseline for what "normal" attribution even looks like in this book.