Mass index
A range-based indicator that flags when the high-low range widens sharply and then contracts, a pattern its creator linked to trend reversals.
What the mass index is.
One line, in a window below price, built only from each bar’s high-low range.
The mass index looks at one thing: the distance between each bar’s high and low. It ignores the open and the close completely.
Donald Dorsey designed it to spot range expansion. His idea was that a sharp widening of the range, followed by a narrowing, often comes near a turning point.
The index does not tell you whether that turn will be up or down. Traders use other tools, such as a moving average of price, for direction.
How it is calculated.
Four steps, repeated on every new bar. A custom indicator does the maths for you.
Measure each bar’s range.
Take the high minus the low. The mass index uses nothing else.
Smooth it once.
Take a 9-period exponential moving average of the range. This is the single EMA.
Smooth it again.
Take a 9-period EMA of the single EMA. This is the double EMA, which reacts more slowly.
Divide and add up.
Divide the single EMA by the double EMA, then add up the last 25 of these ratios. That total is the mass index.
Double EMA = 9-period EMA of the single EMA
Ratio = single EMA ÷ double EMA
Mass index = sum of the last 25 ratios
When ranges are steady, the two EMAs are close and each ratio sits near 1. So the 25-bar total usually sits near 25. A reading above 27 means ranges have widened fast.
How to read it.
Four things traders look for. None of them is a signal on its own.
The reversal bulge.
Dorsey’s pattern: the index rises above 27, then falls back below 26.5. The fall back below 26.5 completes the bulge.
Direction comes from elsewhere.
A bulge suggests a turn may be near, not which way. Dorsey suggested pairing it with a 9-period EMA of price to judge direction.
Readings near 25.
Ranges are steady and neither widening nor narrowing much. The index has little to say about the trend.
False bulges.
Ranges can widen around news or in thin trading, then calm down with no turn at all. Many traders wait for price to confirm.
Common mistakes.
Where traders new to the mass index most often go wrong.
Treating a bulge as a buy or sell signal on its own. It says nothing about direction.
Acting as soon as the index crosses 27. The bulge is only complete when it falls back below 26.5.
Expecting a reversal every time. Ranges often widen and narrow inside a trend that simply carries on.
Installing custom code without checking it. Choose a well-reviewed indicator and test it on a demo first.
Using it on MetaTrader 5.
The mass index is not one of MT5’s built-in indicators. You can add it to desktop MT5 as a custom indicator.
Open the Code Base.
In desktop MT5, open the Toolbox window from the View menu and choose the Code Base tab.
Find a mass index indicator.
Search for mass index and pick one with a clear description and good reviews. Download it from there.
Add it to a chart.
It appears in the Navigator window under Indicators. Drag it onto your chart.
Check the settings.
Look for 9 for the EMAs and 25 for the sum, with levels at 27 and 26.5. Setting names can differ between versions.
Questions, answered.
What traders ask most about the mass index.
01Who created the mass index?
02Why 27 and 26.5?
03Does a bulge mean the trend will reverse?
04Can I use the mass index on MT5 mobile?
05Can I practise with it first?
Practise it on a demo.
Add the mass index to a chart on a free MT5 demo and watch how it reacts when ranges widen and narrow.
Trading CFDs on a live account puts your capital at risk and you can lose money. A demo does not.