What the thinkorswim Volume Index Measures
The thinkorswim Volume Index tracks cumulative volume as it builds over time, giving traders a running total of shares or contracts exchanged during a session. Unlike a simple volume bar, the index shows whether the market is accumulating or distributing, and it helps confirm whether price moves are backed by genuine participation or are running on thin volume. It is one of the built-in studies available in the thinkorswim platform, and it works across stocks, futures and options.
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The index rises with every trade, so a steep climb signals heavy involvement. A flat or slowly rising line suggests the move is fragile and could reverse once participants lose interest.
How the Volume Index Is Calculated
The study sums each trade's volume sequentially from the open of the session. The resulting line is a running total that resets at the start of each new day unless you switch to a cumulative chart setting. Because it is an absolute count, the shape of the line matters more than any single number.
- Each tick adds the traded volume to the running total.
- The line steepens when many contracts or shares trade in a short window.
- The line flattens when activity slows, even if price keeps moving.
Reading the Index Alongside Price
The most common use is to compare the Volume Index trend with price action. When price makes a new high and the index also pushes higher, the move has participation behind it. When price rises but the index barely moves, the rally is suspect and may lack conviction. The same logic applies to lows: a new low on weak volume can signal a short-covering bounce rather than a true breakdown.
Volume Index vs. OBV and Other Studies
The thinkorswim Volume Index is often confused with On-Balance Volume (OBV), but they differ in a meaningful way. OBV adds volume on up days and subtracts it on down days, creating a momentum-style oscillator. The Volume Index is cumulative and non-directional, so it tracks total participation without assigning a sign to the move. Traders who want a raw sense of involvement tend to prefer the index; those looking for directional divergence often reach for OBV or the Chaikin Money Flow.
| Study | Directional? | Best For |
|---|---|---|
| Volume Index | No | Measuring total participation and session involvement |
| OBV | Yes | Confirming trend strength and spotting divergences |
| Chaikin Money Flow | Yes | Spotting accumulation and distribution zones |
Using the Index for Breakout Confirmation
Traders watch the Volume Index when a price breakout occurs. A genuine breakout typically shows a sharp spike in the index at the moment of the move, followed by continued volume support as price pushes into new territory. If the index stalls while price extends, the breakout is often false and will fail back into the prior range. The thinkorswim platform lets you overlay the index on the price chart or view it in a separate pane, which makes it easier to spot these divergences in real time.
Customizing the Volume Index in thinkorswim
The default settings work well for most traders, but you can adjust the study to suit your style. You can change the color, line thickness and plot style, or apply the index to different timeframes. For swing traders, using the index on a daily or weekly chart helps filter out intraday noise. Day traders often keep it on a one- or five-minute chart to catch shifts in participation before they show up on price.
Limitations to Keep in Mind
The Volume Index is a cumulative measure, so it always rises in a trending session and can stay flat during consolidation. It does not tell you why volume is high, only that it is. You still need to combine it with price action, support and resistance levels, and other studies to form a complete read. It also resets each session, so comparing index levels across different days requires a cumulative chart setting or a different analytical approach.
Bottom Line
The thinkorswim Volume Index is a straightforward but powerful way to see how much the market is participating in a move. It confirms strong trends, warns of weak ones, and helps you avoid chasing price on thin volume. Used with other tools in the platform, it gives you a clearer picture of whether the market is behind the trade or against it.