diff --git a/calendar.go b/calendar.go
index 818881b..06aff74 100644
--- a/calendar.go
+++ b/calendar.go
@@ -75,12 +75,12 @@ func (this *Calendar) OnEdit (callback func ()) {
 }
 
 func (this *Calendar) prevMonth () {
-	this.time = firstOfMonth(this.time.Add(24 * time.Hour * 40))
+	this.time = firstOfMonth(this.time.Add(24 * time.Hour * -20))
 	this.refresh()
 }
 
 func (this *Calendar) nextMonth () {
-	this.time = firstOfMonth(this.time.Add(24 * time.Hour * -20))
+	this.time = firstOfMonth(this.time.Add(24 * time.Hour * 40))
 	this.refresh()
 }
 
@@ -125,9 +125,9 @@ func (this *Calendar) refresh () {
 
 func (this *Calendar) handleScroll (x, y float64) {
 	if y < 0 {
-		this.nextMonth()
-	} else {
 		this.prevMonth()
+	} else {
+		this.nextMonth()
 	}
 }