diff --git a/README.md b/README.md
index a1eb7cb..a775b24 100644
--- a/README.md
+++ b/README.md
@@ -21,6 +21,7 @@ The following list of indicators are currently supported by this package:
 - [Community Channel Index (CMI)](trend_indicators.md#community-channel-index-cmi)
 - [Double Exponential Moving Average (DEMA)](trend_indicators.md#double-exponential-moving-average-dema)
 - [Exponential Moving Average (EMA)](trend_indicators.md#exponential-moving-average-ema)
+- [Mass Index (MI)](trend_indicators.md#mass-index-mi)
 - [Moving Average Convergence Divergence (MACD)](trend_indicators.md#moving-average-convergence-divergence-macd)
 - [Moving Max](trend_indicators.md#moving-max)
 - [Moving Min](trend_indicators.md#moving-min)
diff --git a/trend_indicators.go b/trend_indicators.go
index ebeb56e..01e5fa3 100644
--- a/trend_indicators.go
+++ b/trend_indicators.go
@@ -178,6 +178,24 @@ func Macd(closing []float64) ([]float64, []float64) {
 	return macd, signal
 }
 
+// The Mass Index (MI) uses the high-low range to identify trend reversals
+// based on range expansions.
+//
+// Singe EMA = EMA(9, Highs - Lows)
+// Double EMA = EMA(9, Single EMA)
+// Ratio = Single EMA / Double EMA
+// MI = Sum(25, Ratio)
+//
+// Returns mi.
+func MassIndex(high, low []float64) []float64 {
+	ema1 := Ema(9, substract(high, low))
+	ema2 := Ema(9, ema1)
+	ratio := divide(ema1, ema2)
+	mi := Sum(25, ratio)
+
+	return mi
+}
+
 // Moving Chande Forecast Oscillator calculates based on
 // the given period.
 //
diff --git a/trend_indicators.md b/trend_indicators.md
index 95e6a3b..349403d 100644
--- a/trend_indicators.md
+++ b/trend_indicators.md
@@ -9,6 +9,7 @@ Trend indicators measure the direction and strength of a trend.
 - [Community Channel Index (CMI)](#community-channel-index-cmi)
 - [Double Exponential Moving Average (DEMA)](#double-exponential-moving-average-dema)
 - [Exponential Moving Average (EMA)](#exponential-moving-average-ema)
+- [Mass Index (MI)](#mass-index-mi)
 - [Moving Average Convergence Divergence (MACD)](#moving-average-convergence-divergence-macd)
 - [Moving Max](#moving-max)
 - [Moving Min](#moving-min)
@@ -124,6 +125,21 @@ The [Ema](https://pkg.go.dev/github.com/cinar/indicator#Ema) function calculates
 result := indicator.Ema(2, []float64{2, 4, 6, 8, 12, 14, 16, 18, 20})
 ```
 
+#### Mass Index (MI)
+
+The [MassIndex](https://pkg.go.dev/github.com/cinar/indicator#MassIndex) uses the high-low range to identify trend reversals based on range expansions.
+
+```
+Singe EMA = EMA(9, Highs - Lows)
+Double EMA = EMA(9, Single EMA)
+Ratio = Single EMA / Double EMA
+MI = Sum(25, Ratio)
+```
+
+```Golang
+result := indicator.MassIndex(high, low)
+```
+
 #### Moving Average Convergence Divergence (MACD)
 
 The [Macd](https://pkg.go.dev/github.com/cinar/indicator#Macd) function calculates a trend-following momentum indicator that shows the relationship between two moving averages of price.
diff --git a/trend_indicators_test.go b/trend_indicators_test.go
index a87b056..7748b89 100644
--- a/trend_indicators_test.go
+++ b/trend_indicators_test.go
@@ -111,6 +111,26 @@ func TestEma(t *testing.T) {
 	}
 }
 
+func TestMassIndex(t *testing.T) {
+	high := []float64{10, 9, 12, 14, 12}
+	low := []float64{6, 7, 9, 12, 10}
+	expected := []float64{1, 1.92, 2.83, 3.69, 4.52}
+
+	result := MassIndex(high, low)
+
+	if len(result) != len(expected) {
+		t.Fatal("result not same size")
+	}
+
+	for i := 0; i < len(result); i++ {
+		actual := math.Round(result[i]*100) / 100
+
+		if actual != expected[i] {
+			t.Fatalf("result %d actual %f expected %f", i, actual, expected[i])
+		}
+	}
+}
+
 func TestMax(t *testing.T) {
 	values := []float64{10, 9, 8, 7, 6, 5, 4, 3, 2, 1}
 	expected := []float64{10, 10, 10, 10, 9, 8, 7, 6, 5}