Overview

The session reset is fundamental to how standard VWAP works and what it measures. At the session open, the cumulative numerator (sum of price-times-volume) and the cumulative denominator (total volume) both go back to zero. The first bar of the new session starts fresh accumulation. By design, the VWAP line at any intraday moment represents only the volume-weighted average of transactions that occurred during the current session, not yesterday's or any prior session's activity.

This makes session VWAP a purely intraday tool. Once the session closes, the prior session's VWAP line has no direct meaning for the next session's participants: it reflects who transacted then, not who is transacting now.

Why the Reset Matters

The reset defines the population of participants the VWAP references. Session VWAP answers: "at what average price has everyone who traded today transacted?" As the session progresses, more participants enter the calculation. By midday, the denominator (total volume) is large enough to stabilize the line against any single large trade. See early session VWAP reliability.

The reset also means session VWAP has no memory of prior sessions. A stock that had a strong up-day yesterday starts today's VWAP calculation from scratch at the first trade. Where yesterday's VWAP ended has no bearing on today's VWAP at the open.

This is the property that limits session VWAP's usefulness for multi-day context. If you want to know where participants who bought since an earnings release are on average positioned, session VWAP cannot answer that question. Anchored VWAP can.

Anchored VWAP: No Daily Reset

Anchored VWAP (sometimes abbreviated AVWAP) applies the same cumulative formula but anchors the start of accumulation to a user-specified event rather than the daily open. Common anchors include:

  • An earnings release date
  • An IPO date
  • A major market high or low
  • A significant gap day
  • Any price event that brought in meaningful volume

Once anchored, the AVWAP accumulates through every subsequent session without resetting. The line represents the average cost of all participants who bought (or sold) since that anchor event. See Anchored VWAP Explained for a complete discussion, and how to choose an anchor for selection criteria.

Limitations and Context

  • Session definition varies by platform. Some platforms define the "session" to include pre-market and after-hours, others use only regular hours. A platform that includes extended-hours data starts accumulating earlier, producing a different VWAP line than a platform using regular hours only. See regular-hours vs. extended-hours VWAP.
  • The default "VWAP" on most platforms is session-based. If a platform labels the indicator simply "VWAP" without further qualification, assume it resets daily. Anchored VWAP typically requires an explicit anchor-setting step.
  • AVWAP carries growing volume weight over time. As more sessions accumulate after the anchor, any single session's volume becomes a smaller fraction of the total. Very old anchors can produce an AVWAP that moves slowly and reflects a large, diffuse population of historical participants.

Frequently Asked Questions

When exactly does VWAP reset?

Standard session VWAP resets at the session open defined by the platform, typically at 9:30 AM ET for US equity regular-session VWAP. The exact reset time varies if the platform includes pre-market trading in its VWAP calculation.

What happens to VWAP at the overnight session?

Session VWAP typically does not extend into the overnight period. When the regular session closes, the VWAP line ends. On the next regular-session open, a new VWAP line begins accumulating from zero. Extended-hours VWAP behavior depends on platform settings.

Can I see yesterday's VWAP on today's chart?

Most platforms display the prior session's ending VWAP level as a horizontal reference line rather than extending the calculation. This horizontal line shows where the prior session's volume-weighted average settled, but it is not a live VWAP; it is a static price level.

What is the difference between VWAP and AVWAP?

VWAP (session VWAP) resets at each session open and reflects only that day's participants. AVWAP (Anchored VWAP) accumulates from a chosen historical event without daily resets, reflecting the average cost of all participants since that event across multiple sessions.

Does VWAP reset matter for backtesting?

Yes. Backtesting a VWAP-based strategy requires clearly specifying the session definition, including the exact reset time. Using different session definitions produces different VWAP values and different trade signals from the same historical data. See the VWAP backtesting checklist for all required specifications.

References

Disclaimer

This page is for educational purposes only and does not constitute investment, financial, or trading advice. VWAP and related indicators reflect historical price and volume data and do not guarantee future results. Swoopr Investment is not a licensed investment advisor; consult a qualified professional before making trading or investment decisions.