--- src/java/org/apache/poi/ss/formula/atp/WorkdayCalculator.java	(revision 74ab8da0fda0cb2814dbc29a535a5b035469ba36)
+++ src/java/org/apache/poi/ss/formula/atp/WorkdayCalculator.java	(revision )
@@ -38,7 +38,7 @@ 
 
     /**
      * Calculate how many workdays are there between a start and an end date, as excel representations, considering a range of holidays.
-     * 
+     *
      * @param start start date.
      * @param end end date.
      * @param holidays an array of holidays.
@@ -53,7 +53,7 @@ 
 
     /**
      * Calculate the workday past x workdays from a starting date, considering a range of holidays.
-     * 
+     *
      * @param start start date.
      * @param workdays number of workdays to be past from starting date.
      * @param holidays an array of holidays.
@@ -76,10 +76,10 @@ 
 		}
 		return endDate.getTime();
 	}
-    
+
     /**
      * Calculates how many days of week past between a start and an end date.
-     * 
+     *
      * @param start start date.
      * @param end end date.
      * @param dayOfWeek a day of week as represented by {@link Calendar} constants.
@@ -96,12 +96,12 @@ 
                 pastDaysOfWeek++;
             }
         }
-        return start < end ? pastDaysOfWeek : -pastDaysOfWeek;
+        return start <= end ? pastDaysOfWeek : -pastDaysOfWeek;
     }
 
     /**
      * Calculates how many holidays in a list are workdays, considering an interval of dates.
-     * 
+     *
      * @param start start date.
      * @param end end date.
      * @param holidays an array of holidays.
@@ -118,7 +118,7 @@ 
                 }
             }
         }
-        return start < end ? nonWeekendHolidays : -nonWeekendHolidays;
+        return start <= end ? nonWeekendHolidays : -nonWeekendHolidays;
     }
 
     /**
--- src/testcases/org/apache/poi/ss/formula/atp/TestWorkdayCalculator.java	(revision 74ab8da0fda0cb2814dbc29a535a5b035469ba36)
+++ src/testcases/org/apache/poi/ss/formula/atp/TestWorkdayCalculator.java	(revision )
@@ -67,6 +67,24 @@ 
         assertEquals(4, WorkdayCalculator.instance.calculateWorkdays(A_FRIDAY, A_WEDNESDAY, new double[]{ A_SATURDAY, A_SUNDAY }));
     }
 
+	@Test
+	public void testCalculateWorkdaysOnSameDayShouldReturn1ForWeekdays() {
+		final double A_MONDAY = DateUtil.getExcelDate(d(2017, 1, 2));
+		assertEquals(1, WorkdayCalculator.instance.calculateWorkdays(A_MONDAY, A_MONDAY, new double[0]));
+	}
+
+	@Test
+	public void testCalculateWorkdaysOnSameDayShouldReturn0ForHolidays() {
+		final double A_MONDAY = DateUtil.getExcelDate(d(2017, 1, 2));
+		assertEquals(0, WorkdayCalculator.instance.calculateWorkdays(A_MONDAY, A_MONDAY, new double[]{ A_MONDAY }));
+	}
+
+	@Test
+	public void testCalculateWorkdaysOnSameDayShouldReturn0ForWeekends() {
+		final double A_SUNDAY = DateUtil.getExcelDate(d(2017, 1, 1));
+		assertEquals(0, WorkdayCalculator.instance.calculateWorkdays(A_SUNDAY, A_SUNDAY, new double[0]));
+	}
+
     @Test
     public void testCalculateWorkdaysNumberOfDays() {
     	double start = 41553.0;
@@ -108,7 +126,7 @@ 
         final double A_SATURDAY = DateUtil.getExcelDate(d(2011, 12, 10));
         assertEquals(1, WorkdayCalculator.instance.pastDaysOfWeek(A_THURSDAY, A_SATURDAY, SATURDAY));
     }
-    
+
     private static Date d(int year, int month, int day) {
         Calendar cal = LocaleUtil.getLocaleCalendar(year, month-1, day, 0, 0, 0);
         return cal.getTime();