diff --git a/internal/calculator/factor_expression.service.go b/internal/calculator/factor_expression.service.go
index 502380a..43d8db2 100644
--- a/internal/calculator/factor_expression.service.go
+++ b/internal/calculator/factor_expression.service.go
@@ -680,7 +680,7 @@ func (h factorMetricsHandler) PricePercentChange(pr *data.PriceCache, symbol str
 }
 
 func percentChange(end, start float64) float64 {
-	return ((end - start) / end) * 100
+	return ((end - start) / start) * 100
 }
 
 func (h factorMetricsHandler) AnnualizedStdevOfDailyReturns(ctx context.Context, pr *data.PriceCache, symbol string, start, end time.Time) (float64, error) {
diff --git a/internal/calculator/metrics.service.go b/internal/calculator/metrics.service.go
index 626d178..5a0d3db 100644
--- a/internal/calculator/metrics.service.go
+++ b/internal/calculator/metrics.service.go
@@ -54,7 +54,7 @@ func CalculateMetrics(backtestResults []BacktestResult, relevantTradingDays []ti
 	numYears := numHours / (365 * 24)
 	annualizedReturn := math.Pow((endValue/startValue), 1/numYears) - 1
 
-	sharpeRatio := annualizedReturn / stdev
+	sharpeRatio := annualizedReturn / annualizedStdev
 
 	return &CalculateMetricsResult{
 		AnnualizedStdev:  annualizedStdev,
diff --git a/internal/calculator/percent_change_test.go b/internal/calculator/percent_change_test.go
new file mode 100644
index 0000000..20e116d
--- /dev/null
+++ b/internal/calculator/percent_change_test.go
@@ -0,0 +1,55 @@
+package calculator
+
+import (
+	"math"
+	"testing"
+)
+
+func Test_percentChange(t *testing.T) {
+	tests := []struct {
+		name     string
+		end      float64
+		start    float64
+		expected float64
+	}{
+		{
+			name:     "simple increase",
+			end:      110,
+			start:    100,
+			expected: 10.0,
+		},
+		{
+			name:     "simple decrease",
+			end:      90,
+			start:    100,
+			expected: -10.0,
+		},
+		{
+			name:     "no change",
+			end:      100,
+			start:    100,
+			expected: 0.0,
+		},
+		{
+			name:     "double",
+			end:      200,
+			start:    100,
+			expected: 100.0,
+		},
+		{
+			name:     "50 percent drop",
+			end:      50,
+			start:    100,
+			expected: -50.0,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got := percentChange(tt.end, tt.start)
+			if math.Abs(got-tt.expected) > 0.0001 {
+				t.Errorf("percentChange(%v, %v) = %v, want %v", tt.end, tt.start, got, tt.expected)
+			}
+		})
+	}
+}
diff --git a/internal/data/percent_change_test.go b/internal/data/percent_change_test.go
new file mode 100644
index 0000000..ebf2d15
--- /dev/null
+++ b/internal/data/percent_change_test.go
@@ -0,0 +1,49 @@
+package data
+
+import (
+	"math"
+	"testing"
+)
+
+func Test_percentChange(t *testing.T) {
+	tests := []struct {
+		name     string
+		end      float64
+		start    float64
+		expected float64
+	}{
+		{
+			name:     "simple increase",
+			end:      110,
+			start:    100,
+			expected: 10.0,
+		},
+		{
+			name:     "simple decrease",
+			end:      90,
+			start:    100,
+			expected: -10.0,
+		},
+		{
+			name:     "no change",
+			end:      100,
+			start:    100,
+			expected: 0.0,
+		},
+		{
+			name:     "double",
+			end:      200,
+			start:    100,
+			expected: 100.0,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got := percentChange(tt.end, tt.start)
+			if math.Abs(got-tt.expected) > 0.0001 {
+				t.Errorf("percentChange(%v, %v) = %v, want %v", tt.end, tt.start, got, tt.expected)
+			}
+		})
+	}
+}
diff --git a/internal/data/price.service.go b/internal/data/price.service.go
index db51c98..a001173 100644
--- a/internal/data/price.service.go
+++ b/internal/data/price.service.go
@@ -97,7 +97,7 @@ func (pr *PriceCache) Get(symbol string, date time.Time) (float64, error) {
 }
 
 func percentChange(end, start float64) float64 {
-	return ((end - start) / end) * 100
+	return ((end - start) / start) * 100
 }
 
 func stdevsFromPriceMap(minMaxMap map[string]*minMax, priceCache map[string]map[string]float64, stdevInputs []LoadStdevCacheInput, tradingDays []time.Time) (*stdevCache, error) {