diff --git a/htdocs/compta/facture/class/facture.class.php b/htdocs/compta/facture/class/facture.class.php
index 24f5b748e52..f036145161d 100644
--- a/htdocs/compta/facture/class/facture.class.php
+++ b/htdocs/compta/facture/class/facture.class.php
@@ -1191,23 +1191,23 @@ class Facture extends CommonInvoice
 			{
 				unset($object->lines[$i]);
 			}
-						// Bloc to update dates of service (month by month only if previously filled at 1d near start or end of month)
+
+			// Bloc to update dates of service (month by month only if previously filled and similare to start and end of month)
 			// If it's a service with start and end dates
-			if (!empty($line->date_start) && !empty($line->date_end)) {
+			if (!empty($conf->global->INVOICE_AUTO_NEXT_MONTH_ON_LINES) && !empty($line->date_start) && !empty($line->date_end)) {
 				// Get the dates
 				$start = dol_getdate($line->date_start);
 				$end = dol_getdate($line->date_end);
 
 				// Get the first and last day of the month
 				$first = dol_get_first_day($start['year'], $start['mon']);
-				$last = dol_get_first_day($end['year'], $end['mon']);
+				$last = dol_get_last_day($end['year'], $end['mon']);
 
-				// Get diff betweend start/end of month and previously filled
-				$diffFirst = num_between_day($first, dol_mktime($start['hours'], $start['minutes'], $start['seconds'], $start['mon'], $start['mday'], $start['year'], 'user'));
-				$diffLast = num_between_day(dol_mktime($end['hours'], $end['minutes'], $end['seconds'], $end['mon'], $end['mday'], $end['year'], 'user'), $last);
-
-				// If there is <= 1d (or 2?) of start/or/end of month
-				if ($diffFirst <= 2 && $diffLast <= 2) {
+				//print dol_print_date(dol_mktime(0, 0, 0, $start['mon'], $start['mday'], $start['year'], 'gmt'), 'dayhour').' '.dol_print_date($first, 'dayhour').'<br>';
+				//print dol_mktime(23, 59, 59, $end['mon'], $end['mday'], $end['year'], 'gmt').' '.$last.'<br>';exit;
+				// If start date is first date of month and end date is last date of month
+				if (dol_mktime(0, 0, 0, $start['mon'], $start['mday'], $start['year'], 'gmt') == $first
+					&& dol_mktime(23, 59, 59, $end['mon'], $end['mday'], $end['year'], 'gmt') == $last) {
 					$nextMonth = dol_get_next_month($end['mon'], $end['year']);
 					$newFirst = dol_get_first_day($nextMonth['year'], $nextMonth['month']);
 					$newLast = dol_get_last_day($nextMonth['year'], $nextMonth['month']);
diff --git a/htdocs/core/lib/date.lib.php b/htdocs/core/lib/date.lib.php
index 3a889367dc1..74b091865ff 100644
--- a/htdocs/core/lib/date.lib.php
+++ b/htdocs/core/lib/date.lib.php
@@ -356,7 +356,8 @@ function dol_stringtotime($string, $gm = 1)
 }
 
 
-/** Return previous day
+/**
+ *  Return previous day
  *
  *  @param      int			$day     	Day
  *  @param      int			$month   	Month
@@ -371,7 +372,8 @@ function dol_get_prev_day($day, $month, $year)
 	return array('year' => $tmparray['year'], 'month' => $tmparray['mon'], 'day' => $tmparray['mday']);
 }
 
-/** Return next day
+/**
+ *  Return next day
  *
  *  @param      int			$day    	Day
  *  @param      int			$month  	Month
@@ -386,7 +388,8 @@ function dol_get_next_day($day, $month, $year)
 	return array('year' => $tmparray['year'], 'month' => $tmparray['mon'], 'day' => $tmparray['mday']);
 }
 
-/**	Return previous month
+/**
+ *  Return previous month
  *
  *	@param		int			$month		Month
  *	@param		int			$year		Year
@@ -405,7 +408,8 @@ function dol_get_prev_month($month, $year)
 	return array('year' => $prev_year, 'month' => $prev_month);
 }
 
-/**	Return next month
+/**
+ *  Return next month
  *
  *	@param		int			$month		Month
  *	@param		int			$year		Year
@@ -424,7 +428,8 @@ function dol_get_next_month($month, $year)
 	return array('year' => $next_year, 'month' => $next_month);
 }
 
-/**	Return previous week
+/**
+ *  Return previous week
  *
  *  @param      int			$day     	Day
  *  @param      int			$week    	Week
@@ -442,7 +447,8 @@ function dol_get_prev_week($day, $week, $month, $year)
 	return array('year' => $tmparray['year'], 'month' => $tmparray['mon'], 'day' => $tmparray['mday']);
 }
 
-/**	Return next week
+/**
+ *  Return next week
  *
  *  @param      int			$day     	Day
  *  @param      int			$week    	Week
@@ -461,7 +467,8 @@ function dol_get_next_week($day, $week, $month, $year)
 	return array('year' => $tmparray['year'], 'month' => $tmparray['mon'], 'day' => $tmparray['mday']);
 }
 
-/**	Return GMT time for first day of a month or year
+/**
+ *  Return GMT time for first day of a month or year
  *
  *	@param		int			$year		Year
  * 	@param		int			$month		Month
@@ -478,7 +485,9 @@ function dol_get_first_day($year, $month = 1, $gm = false)
 }
 
 
-/**	Return GMT time for last day of a month or year
+/**
+ * Return GMT time for last day of a month or year.
+ * Note: The timestamp contains last day and last hours (23:59:59)
  *
  *	@param		int			$year		Year
  * 	@param		int			$month		Month
@@ -504,7 +513,8 @@ function dol_get_last_day($year, $month = 12, $gm = false)
 	return $datelim;
 }
 
-/**	Return GMT time for last hour of a given GMT date (it removes hours, min and second part)
+/**
+ *  Return GMT time for last hour of a given GMT date (it removes hours, min and second part)
  *
  *	@param		int			$date		Date
  *  @return		int						Date for last hour of a given date
@@ -515,7 +525,8 @@ function dol_get_last_hour($date)
 	return dol_mktime(23, 59, 59, $tmparray['mon'], $tmparray['mday'], $tmparray['year'], false);
 }
 
-/**	Return GMT time for first hour of a given GMT date (it removes hours, min and second part)
+/**
+ *  Return GMT time for first hour of a given GMT date (it removes hours, min and second part)
  *
  *	@param		int			$date		Date
  *  @return		int						Date for last hour of a given date