TWAP (time-weighted average price)

What it means

A TWAP benchmark gives each equally spaced price observation the same weight, regardless of how many shares traded at that time. For example, an hourly observation counts as much as every other hourly observation in the chosen period. The result describes an average price over time, not a price available for every share in an order.

TWAP can also mean an execution schedule: dividing an order into smaller pieces intended to trade at a roughly constant rate across a specified window. An evenly timed schedule is not guaranteed to achieve the TWAP benchmark. Actual fills depend on available liquidity, order types, market movement, and whether each piece executes.

How it is calculated

For prices sampled at equal time intervals, the simple benchmark is:

TWAP = (P₁ + P₂ + ... + Pₙ) / n

• P₁ ... Pₙ are the observed prices in the selected period, in US$ per share for a US stock. Use a consistent price measure, such as the last traded price at each observation time.
• n is the number of equally spaced observations. It has no units.
• TWAP is in US$ per share. The window and sampling frequency must be stated alongside the figure.

For a hypothetical schedule of equal-sized pieces at equal time intervals, the target for each piece is Q / n, where Q is the total order quantity in shares and n is the number of pieces. This is a scheduling rule, not the benchmark-price formula. If observed prices are sampled at uneven intervals, their simple average is not strictly time-weighted; use observations on an equal-time grid or weight observations by their represented durations.

Worked example

Suppose a hypothetical US stock has four hourly price observations during a four-hour window: US$50.00, US$50.20, US$49.80, and US$50.40 per share.

1. Add the observations: US$50.00 + US$50.20 + US$49.80 + US$50.40 = US$200.40 per share.
2. Divide by four: TWAP = US$50.10 per share.
3. Separately, a hypothetical 400-share order spread into four equal pieces would target 100 shares per piece, one each hour.

US$50.10 is the observed-price benchmark, not necessarily the order’s average fill price. If the four pieces actually fill at US$50.10, US$50.30, US$49.90, and US$50.50, their equal-share average fill is US$50.20 per share. For a buy order, that is US$0.10 per share, or US$40 across 400 shares, above the benchmark. This arithmetic excludes commissions and other costs; different fill quantities would require a share-weighted average fill price.

Why it matters before you trade

A TWAP schedule spreads an order through time rather than requesting the full quantity at once. That may be relevant when an order is large relative to available liquidity, but spreading it does not eliminate bid-ask spread, market impact, or price-movement risk. A fixed schedule may also trade when volume is thin; unlike a VWAP schedule, it does not automatically allocate more of the order to high-volume periods.

Before placing an order, useful checks include order size relative to daily volume, the estimated spread and market impact, the intended trading window, and the possibility of partial fills. Comparing an eventual fill with TWAP answers a different question from comparing it with the arrival price: a moving market can change the time-average benchmark even without an unusually costly execution.

How PreTrAIde uses it

The product facts do not say that PreTrAIde calculates a TWAP benchmark, offers a TWAP execution algorithm, or routes orders. Its pre-trade analysis can instead inform an execution decision: for a user-built stock basket, it estimates spread, participation in daily volume, and market impact, and returns a suggested execution strategy with its reasoning. Its GO, NO-GO, or MODIFY verdicts are decision support, not recommendations. Users place any orders themselves through their own broker.

Common mistakes

• Confusing TWAP with VWAP. TWAP weights equally spaced times equally; VWAP weights prices by shares traded.
• Treating scheduled pieces as guaranteed fills. A limit order might not execute, while a market order’s fill price can differ from the sampled price.
• Ignoring the chosen window. Different start times, end times, or sampling methods can produce different benchmarks.
• Calling benchmark slippage the total cost. A comparison with TWAP alone does not capture every spread, commission, market-impact, or opportunity cost.