diff --git a/internal/display/formatter.go b/internal/display/formatter.go
index 7208083..83198ec 100644
--- a/internal/display/formatter.go
+++ b/internal/display/formatter.go
@@ -2,15 +2,32 @@ package display
 
 import (
 	"fmt"
+	"strings"
 	"time"
 )
 
 // FormatCurrency formats a float as currency with comma separators
 func FormatCurrency(amount float64) string {
+	sign := ""
 	if amount < 0 {
-		return fmt.Sprintf("-$%.2f", -amount)
+		sign = "-"
+		amount = -amount
 	}
-	return fmt.Sprintf("$%.2f", amount)
+
+	formatted := fmt.Sprintf("%.2f", amount)
+	parts := strings.Split(formatted, ".")
+	intPart := parts[0]
+	decimalPart := parts[1]
+
+	var withCommas strings.Builder
+	for i, digit := range intPart {
+		if i > 0 && (len(intPart)-i)%3 == 0 {
+			withCommas.WriteByte(',')
+		}
+		withCommas.WriteRune(digit)
+	}
+
+	return fmt.Sprintf("%s$%s.%s", sign, withCommas.String(), decimalPart)
 }
 
 // FormatPercent formats a float as a percentage
diff --git a/internal/display/formatter_test.go b/internal/display/formatter_test.go
new file mode 100644
index 0000000..d41ad9e
--- /dev/null
+++ b/internal/display/formatter_test.go
@@ -0,0 +1,25 @@
+package display
+
+import (
+	"fmt"
+	"testing"
+)
+
+func TestFormatCurrencyAddsCommas(t *testing.T) {
+	tests := []struct {
+		amount float64
+		want   string
+	}{
+		{1234.56, "$1,234.56"},
+		{9876543.2, "$9,876,543.20"},
+		{-1200.5, "-$1,200.50"},
+	}
+
+	for _, tt := range tests {
+		t.Run(fmt.Sprintf("%v", tt.amount), func(t *testing.T) {
+			if got := FormatCurrency(tt.amount); got != tt.want {
+				t.Fatalf("FormatCurrency(%v) = %q, want %q", tt.amount, got, tt.want)
+			}
+		})
+	}
+}