diff --git a/htdocs/cron/card.php b/htdocs/cron/card.php
index 87a054c699f..5de627a9a9a 100644
--- a/htdocs/cron/card.php
+++ b/htdocs/cron/card.php
@@ -473,6 +473,16 @@ if (($action == "create") || ($action == "edit")) {
 	}
 	$input .= "<label for=\"frequency_semaine\">".$langs->trans('Weeks')."</label>";
 	print $input;
+
+	$input = " <input type=\"radio\" name=\"unitfrequency\" value=\"2678400\" id=\"frequency_month\" ";
+	if ($object->unitfrequency == "2678400") {
+		$input .= ' checked />';
+	} else {
+		$input .= ' />';
+	}
+	$input .= "<label for=\"frequency_month\">".$langs->trans('Monthly')."</label>";
+	print $input;
+
 	print "</td>";
 	print "<td>";
 	print "</td>";
@@ -664,6 +674,9 @@ if (($action == "create") || ($action == "edit")) {
 	if ($object->unitfrequency == "604800") {
 		print $langs->trans('CronEach')." ".($object->frequency)." ".$langs->trans('Weeks');
 	}
+	if ($object->unitfrequency == "2678400") {
+		print $langs->trans('CronEach')." ".($object->frequency)." ".$langs->trans('Month');
+	}
 	print "</td></tr>";
 
 	print '<tr><td>';
diff --git a/htdocs/cron/class/cronjob.class.php b/htdocs/cron/class/cronjob.class.php
index db48c0e7fce..8f4b32ae502 100644
--- a/htdocs/cron/class/cronjob.class.php
+++ b/htdocs/cron/class/cronjob.class.php
@@ -1,5 +1,5 @@
 <?php
-/* Copyright (C) 2007-2019 Laurent Destailleur  <eldy@users.sourceforge.net>
+/* Copyright (C) 2007-2022 Laurent Destailleur  <eldy@users.sourceforge.net>
  * Copyright (C) 2013      Florian Henry        <florian.henry@open-concept.pro>
  *
  * This program is free software; you can redistribute it and/or modify
@@ -23,6 +23,7 @@
 
 // Put here all includes required by your class file
 require_once DOL_DOCUMENT_ROOT."/core/class/commonobject.class.php";
+require_once DOL_DOCUMENT_ROOT."/core/lib/date.lib.php";
 
 
 /**
@@ -1408,21 +1409,30 @@ class Cronjob extends CommonObject
 
 		if (empty($this->datenextrun)) {
 			if (empty($this->datestart)) {
-				$this->datenextrun = $now + ($this->frequency * $this->unitfrequency);
+				if ($this->unitfrequency == 2678400) {
+					$this->datenextrun = dol_time_plus_duree($now, $this->frequency, 'm');
+				} else {
+					$this->datenextrun = $now + ($this->frequency * $this->unitfrequency);
+				}
 			} else {
-				$this->datenextrun = $this->datestart + ($this->frequency * $this->unitfrequency);
+				if ($this->unitfrequency == 2678400) {
+					$this->datenextrun = dol_time_plus_duree($this->datestart, $this->frequency, 'm');
+				} else {
+					$this->datenextrun = $this->datestart + ($this->frequency * $this->unitfrequency);
+				}
 			}
 		}
 
 		if ($this->datenextrun < $now && $this->frequency > 0 && $this->unitfrequency > 0) {
 			// Loop until date is after future
 			while ($this->datenextrun < $now) {
-				$this->datenextrun += ($this->frequency * $this->unitfrequency);
-
-				// TODO For exact frequency (every month, every year, ...), use instead a dol_time_plus_duree($time, $duration_value, $duration_unit)
+				if ($this->unitfrequency == 2678400) {
+					$this->datenextrun = dol_time_plus_duree($this->datenextrun, $this->frequency, 'm');
+				} else {
+					$this->datenextrun += ($this->frequency * $this->unitfrequency);
+				}
 			}
 		} else {
-			//$this->datenextrun=$this->datenextrun + ($this->frequency * $this->unitfrequency);
 			dol_syslog(get_class($this)."::reprogram_jobs datenextrun is already in future, we do not change it");
 		}