diff --git a/src/action/UsageInterval.php b/src/action/UsageInterval.php
index a1280d9f..4f4fba0a 100644
--- a/src/action/UsageInterval.php
+++ b/src/action/UsageInterval.php
@@ -110,9 +110,9 @@ public static function withMonthAndFraction(
         if ($fractionOfMonth === 1.0) {
             $effectiveTill = $month->modify('+1 month');
         } else {
-            $monthDays = (int) $month->format('t');
-            $days = (int) round($monthDays * $fractionOfMonth);
-            $effectiveTill = $effectiveSince->modify(sprintf('+%d days', $days));
+            $interval = new self($month, $nextMonth);
+            $seconds = $interval->secondsInMonth() * $fractionOfMonth;
+            $effectiveTill = $effectiveSince->modify(sprintf('+%d seconds', $seconds));
         }
 
         return new self(
diff --git a/tests/unit/action/UsageIntervalTest.php b/tests/unit/action/UsageIntervalTest.php
index e8224af0..911654e2 100644
--- a/tests/unit/action/UsageIntervalTest.php
+++ b/tests/unit/action/UsageIntervalTest.php
@@ -227,9 +227,9 @@ public function provideWithMonthAndFraction()
             [
                 'start' => '2024-02-01 11:50:00',
                 'end' => '2024-02-29 18:15:00',
-                'ratioOfMonth' => 0.97473659003831,
-                'seconds' => 2_419_200,
-                'secondsInMonth' => 2_419_200,
+                'ratioOfMonth' => 0.9747365900383141,
+                'seconds' => 2_442_300,
+                'secondsInMonth' => 2_505_600,
             ]
         ];
     }