diff --git a/ostat.go b/ostat.go
index ecbbad8..002ed27 100644
--- a/ostat.go
+++ b/ostat.go
@@ -95,6 +95,13 @@ func (os *OnlineStat) StdDev() float64 {
 	return math.Sqrt(os.Variance())
 }
 
+func (os *OnlineStat) CI() (float64, float64) {
+	// 95% from http://mathworld.wolfram.com/ConfidenceInterval.html
+	conf := 1.95996
+	dev := os.StdDev() / math.Sqrt(float64(os.n))
+	return os.mean - dev*conf, os.mean + dev*conf
+}
+
 func (os *OnlineStat) String() string {
 	return fmt.Sprintf(
 		"%+v",