What is Post-trade drift?

Post-trade drift is the price movement observed after an order or program finishes. It is used to evaluate whether fills were followed by adverse or favorable moves beyond what the market was already doing.

This analysis helps identify selection effects and whether timing created avoidable costs.

Diagnosing what moved

Analysts compare post-trade windows to pre-trade baselines and to market controls. If prices continue moving against the trade after completion, selection or residual impact may be present. If prices revert, prior moves may have been impact rather than information.

Window choice, controls, and volatility normalization are critical to fair diagnosis.

Strategy feedback loops

Findings influence routing, order type mix, and aggressiveness. Persistent adverse drift on certain venues suggests reducing passive exposure there. If drift is neutral where depth refill is fast, posting may be safer.

Desks review drift by size, time of day, and asset to avoid overgeneralizing from isolated events.

Limits to attribution

Attribution is inherently uncertain. Correlated flows, news, and data issues can confound results. Mis-specified windows or benchmarks can label normal noise as drift.

Teams document assumptions, rerun analyses periodically, and remain cautious about causal claims.

Things to Remember

• Look after you finish: Post-trade windows reveal selection or residual impact.
• Control the context: Use market controls and volatility scaling for fairness.
• Act on patterns: Adjust routing or tactics where adverse drift clusters.
• Stay skeptical: Attribution is noisy; avoid hard conclusions from few samples.