What is VWAP and why is it used as an execution benchmark?

Question

AcadiFi · Accepted Answer

VWAP stands for Volume-Weighted Average Price: the average price of a stock during a period, weighted by traded volume at each price.

Formula: VWAP = Σ(Price_i × Volume_i) / Σ(Volume_i)

Over a full trading day with trades at $42.00 (100k shares), $42.10 (300k), $42.20 (200k), VWAP = (42.00×100k + 42.10×300k + 42.20×200k) / 600k = $42.117.

Execution quality comparison: if trader Petra Lindqvist filled 50k shares of her buy order at an average $42.08 against a full-day VWAP of $42.117, she beat VWAP by ~3.7¢ per share — interpreted as favorable execution.

Why VWAP dominates as a benchmark:

1. **Passive-friendly** — a broker can literally aim to match VWAP by participating with volume throughout the day.
2. **Post-trade observable** — computable from public tape without any private info.
3. **Fair** — it reflects actual market conditions, so missing it signals bad execution rather than bad luck.
4. **Scales across names** — percentile rankings are stable across liquid stocks.

Limitations:

- Participating with volume to match VWAP *causes* impact, so 'beating VWAP' can be illusory.
- VWAP says nothing about whether you should have traded at all.
- A large order whose own volume dominates the day's tape will mechanically approach VWAP, masking impact.

For a more decision-oriented metric, traders use Implementation Shortfall (Perold), which measures deviation from arrival price rather than a volume-weighted benchmark. VWAP remains best for brokers showing execution consistency, while IS suits portfolio managers measuring opportunity cost.

What is VWAP and why is it used as an execution benchmark?

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