diff --git a/util.go b/util.go
index ee362fa..d5ee31a 100644
--- a/util.go
+++ b/util.go
@@ -6,7 +6,7 @@ import (
 
 func toDate(d uint32) time.Time {
 	t, _ := time.Parse("2006-01-02T15:04:05+07:00", "0000-01-01 00:00:00+00:00")
-	t = t.AddDate(0, 0, int(d))
+	t = t.AddDate(0, 0, int(d-1))
 	return t
 }