diff --git a/index.php b/index.php
index 2733deb..855a593 100644
--- a/index.php
+++ b/index.php
@@ -347,23 +347,8 @@ function buildNewsletterHtml(array $config, array $articles, string $periodLabel
         ? 'Im Zeitraum ' . h($periodLabel) . ' wurde 1 neuer Wiki-Artikel veröffentlicht.'
         : 'Im Zeitraum ' . h($periodLabel) . ' wurden ' . $count . ' neue Wiki-Artikel veröffentlicht.';
 
-    $dateRangeText = 'für den Zeitraum ' . h($periodLabel);
-    if (!empty($articles)) {
-        $timestamps = [];
-        foreach ($articles as $article) {
-            $date = DateTimeImmutable::createFromFormat('Y-m-d', (string)($article['date'] ?? ''));
-            if ($date instanceof DateTimeImmutable) {
-                $timestamps[] = $date->getTimestamp();
-            }
-        }
-
-        if (!empty($timestamps)) {
-            sort($timestamps);
-            $from = (new DateTimeImmutable('@' . (string)$timestamps[0]))->setTimezone(new DateTimeZone(date_default_timezone_get()));
-            $to = (new DateTimeImmutable('@' . (string)$timestamps[count($timestamps) - 1]))->setTimezone(new DateTimeZone(date_default_timezone_get()));
-            $dateRangeText = 'vom ' . $from->format('d.m.Y') . ' bis ' . $to->format('d.m.Y');
-        }
-    }
+    [$periodStart, $periodEnd] = newsletterPeriod((string)$config['period_mode']);
+    $dateRangeText = 'vom ' . $periodStart->format('d.m.Y') . ' bis ' . $periodEnd->format('d.m.Y');
 
     $articleRows = '';
     if ($count === 0) {
diff --git a/wiki.php b/wiki.php
index f30e226..95347d1 100644
--- a/wiki.php
+++ b/wiki.php
@@ -347,23 +347,8 @@ function buildNewsletterHtml(array $config, array $articles, string $periodLabel
         ? 'Im Zeitraum ' . h($periodLabel) . ' wurde 1 neuer Wiki-Artikel veröffentlicht.'
         : 'Im Zeitraum ' . h($periodLabel) . ' wurden ' . $count . ' neue Wiki-Artikel veröffentlicht.';
 
-    $dateRangeText = 'für den Zeitraum ' . h($periodLabel);
-    if (!empty($articles)) {
-        $timestamps = [];
-        foreach ($articles as $article) {
-            $date = DateTimeImmutable::createFromFormat('Y-m-d', (string)($article['date'] ?? ''));
-            if ($date instanceof DateTimeImmutable) {
-                $timestamps[] = $date->getTimestamp();
-            }
-        }
-
-        if (!empty($timestamps)) {
-            sort($timestamps);
-            $from = (new DateTimeImmutable('@' . (string)$timestamps[0]))->setTimezone(new DateTimeZone(date_default_timezone_get()));
-            $to = (new DateTimeImmutable('@' . (string)$timestamps[count($timestamps) - 1]))->setTimezone(new DateTimeZone(date_default_timezone_get()));
-            $dateRangeText = 'vom ' . $from->format('d.m.Y') . ' bis ' . $to->format('d.m.Y');
-        }
-    }
+    [$periodStart, $periodEnd] = newsletterPeriod((string)$config['period_mode']);
+    $dateRangeText = 'vom ' . $periodStart->format('d.m.Y') . ' bis ' . $periodEnd->format('d.m.Y');
 
     $articleRows = '';
     if ($count === 0) {