What it does
The Mass Index, developed by Donald Dorsey, detects potential trend reversals by measuring the expansion and contraction of the daily high-low range, ignoring direction entirely. It takes a 9-period EMA of the high-low range, divides it by a 9-period EMA of that EMA, and sums this ratio over 25 periods. When ranges widen sharply the sum rises, signaling volatility that often precedes a reversal.
Typeoscillatorseparate pane
How to add it
Click Indicators (ƒx) in the header.
Search “Mass Index” and click the result.
Hover its legend row and click the gear to open settings.
How traders use it
- Watch for the classic reversal bulge: the Mass Index rises above 27 and then falls back below 26.5, which flags a likely trend change without saying which direction.
- Because the indicator is direction-blind, determine the reversal direction with a separate tool such as a 9-period EMA of price or the prevailing trend slope.
- Low, flat readings indicate range compression and quiet conditions that often precede a breakout; some traders use this as a volatility squeeze warning.
- It was designed on daily data; on intraday charts recalibrate the 27 and 26.5 thresholds to the instrument's typical range behavior.
Inputs
| Input | Type | Default | Range / Options |
|---|---|---|---|
| Length | number | 10 | 1–2000 |
Plots & styling
| Plot | Style | Default color |
|---|---|---|
| Mass Index | line | #2196F3 |
Every plot's color, line width and visibility can be changed on the Style tab. Precision (default 2 decimals), price-scale labels and status-line values are configurable at the bottom of the Style tab.
Tips
- Hide the study from the legend eye instead of removing it when you only want it out of the way temporarily.
- Merge multiple oscillators into one pane from the legend ⋯ menu to compare them on a shared axis.
- Double-click the plot to open settings directly, skipping the legend hover.
Watch out for
- The reversal bulge fires relatively rarely and gives no directional bias, so it is unusable as a standalone entry signal.
- Volatility expansions also occur in strong trend continuations, so a bulge can mark acceleration rather than reversal.