VWAP and TWAP Execution Algorithms Explained

VWAP tracks the market's own volume curve while TWAP slices an order evenly through time, and the choice changes who bears the risk.

VWAP and TWAP are the two oldest scheduling benchmarks in electronic execution. A volume weighted average price algorithm slices an order to track the market's own volume pattern through the session, while a time weighted average price algorithm splits the same order into equal clips at fixed intervals regardless of how much volume is trading around it.

A VWAP algorithm forecasts what share of the day's total volume is likely to trade in each interval, using a historical curve for that stock, and then sizes its own clips to match that share. If the model expects 8 percent of the day's volume to trade in a given half hour window, the algorithm aims to place roughly 8 percent of the parent order in that same window.

The benchmark it is graded against is the volume weighted average price of the entire session, so an algorithm that finishes above the VWAP on a buy order is judged to have traded expensively relative to the rest of the market, independent of whether the stock rose or fell that day.

A TWAP algorithm ignores the volume curve entirely and instead divides the order into equal pieces spread evenly across a chosen time window, trading a fixed clip every minute or every five minutes until the order is complete. It is a simpler, more predictable schedule, and it is used deliberately when a trader wants to avoid tying execution to a volume forecast that could be wrong, particularly around a stock with an unusual or event-driven volume pattern that day.

Equity volume across a session typically forms a U shape: a large share of the day's volume trades in the first thirty minutes after the open, volume falls to its lowest point through the middle of the day, and it rises again into the close. Reported curves commonly show something like 15 to 20 percent of the day's volume concentrated in the opening half hour and a similar share in the closing half hour, with the remaining volume spread thinly across the middle hours.