Index: src/main/java/com/xpn/xwiki/stats/impl/XWikiStats.java
===================================================================
--- src/main/java/com/xpn/xwiki/stats/impl/XWikiStats.java	(revision 5418)
+++ src/main/java/com/xpn/xwiki/stats/impl/XWikiStats.java	(working copy)
@@ -53,13 +53,18 @@
         setIntValue("period", period);
     }
 
-    public int getPeriodAsInt(Date date, int type) {
+    public static int getPeriodAsInt(Date date, int type) {
         Calendar cal = Calendar.getInstance();
-        cal.setTime(date);
-        if (type == PERIOD_MONTH)
-         return cal.get(Calendar.YEAR) * 100 + (cal.get(Calendar.MONTH)+1);
-       else
-         return cal.get(Calendar.YEAR) * 10000 + (cal.get(Calendar.MONTH)+1) * 100 + (cal.get(Calendar.DAY_OF_MONTH)+1);
+        if (date != null){
+            cal.setTime(date);
+        }
+        if (type == PERIOD_MONTH){
+            // The first month of the year is JANUARY which is 0
+            return cal.get(Calendar.YEAR) * 100 + (cal.get(Calendar.MONTH)+1);
+        } else {
+            // The first day of the month has value 1
+            return cal.get(Calendar.YEAR) * 10000 + (cal.get(Calendar.MONTH)+1) * 100 + cal.get(Calendar.DAY_OF_MONTH);
+        }
     }
 
     public int getPageViews() {
Index: src/test/java/com/xpn/xwiki/stats/impl/XWikiStatsTest.java
===================================================================
--- src/test/java/com/xpn/xwiki/stats/impl/XWikiStatsTest.java	(revision 0)
+++ src/test/java/com/xpn/xwiki/stats/impl/XWikiStatsTest.java	(revision 0)
@@ -0,0 +1,51 @@
+/*
+ * See the NOTICE file distributed with this work for additional
+ * information regarding copyright ownership.
+ *
+ * This is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU Lesser General Public License as
+ * published by the Free Software Foundation; either version 2.1 of
+ * the License, or (at your option) any later version.
+ *
+ * This software is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this software; if not, write to the Free
+ * Software Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA
+ * 02110-1301 USA, or see the FSF site: http://www.fsf.org.
+ */
+package com.xpn.xwiki.stats.impl;
+
+import java.text.SimpleDateFormat;
+import java.util.Calendar;
+
+import junit.framework.TestCase;
+
+/**
+ * Unit tests for the {@link XWikiStats} class.
+ * 
+ * @version $Id: $
+ */
+public class XWikiStatsTest extends TestCase
+{
+    /**
+     * Test for the {@link XWikiStats#getPeriodAsInt(java.util.Date, int)}
+     */
+    public void testGetPeriodAsInt()
+    {
+        Calendar cal = Calendar.getInstance();
+
+        SimpleDateFormat sdf = new SimpleDateFormat("yyyyMM");
+        String a = sdf.format(cal.getTime());
+        String b = XWikiStats.getPeriodAsInt(cal.getTime(), XWikiStats.PERIOD_MONTH) + "";
+        assertTrue("Wrong month period format", a.equals(b));
+
+        sdf = new SimpleDateFormat("yyyyMMdd");
+        a = sdf.format(cal.getTime());
+        b = XWikiStats.getPeriodAsInt(cal.getTime(), XWikiStats.PERIOD_DAY) + "";
+        assertTrue("Wrong day period format", a.equals(b));
+    }
+}