diff --git a/src/BusinessTime.php b/src/BusinessTime.php
index 93d618c..98ba9e9 100644
--- a/src/BusinessTime.php
+++ b/src/BusinessTime.php
@@ -46,7 +46,22 @@ public function isBusinessTime(): bool
      */
     public function isBusinessDay(): bool
     {
-        return $this->startOfBusinessDay()->isSameDay($this);
+        // Must be a business day if it's business time right now.
+        if ($this->isBusinessTime()) {
+            return true;
+        }
+
+        // Iterate from the beginning of the day until we hit business time.
+        $time = $this->copy()->startOfDay();
+        $end = $this->copy()->endOfDay();
+        while ($time->lt($end)) {
+            if ($time->isBusinessTime()) {
+                return true;
+            }
+            $time = $time->add($this->precision());
+        }
+
+        return false;
     }
 
     /**
@@ -106,6 +121,11 @@ public function addBusinessDays(float $businessDaysToAdd): self
             $next = $next->add($this->precision());
         }
 
+        // Ensure we always end on a business day.
+        while (!$next->isBusinessDay()) {
+            $next = $next->addDay();
+        }
+
         return $next;
     }
 
@@ -161,6 +181,11 @@ public function subBusinessDays(float $businessDaysToSub): self
             }
         }
 
+        // Ensure we always end on a business day.
+        while (!$prev->isBusinessDay()) {
+            $prev = $prev->subDay();
+        }
+
         return $prev;
     }
 
diff --git a/tests/Unit/BusinessTime/AddBusinessDaysTest.php b/tests/Unit/BusinessTime/AddBusinessDaysTest.php
index 44bdcb8..76c0f79 100644
--- a/tests/Unit/BusinessTime/AddBusinessDaysTest.php
+++ b/tests/Unit/BusinessTime/AddBusinessDaysTest.php
@@ -57,6 +57,7 @@ public function addBusinessDayProvider(): array
             ['Friday 2018-05-18 14:00', 'Monday 2018-05-21 14:00'],
             ['Saturday 2018-05-19 15:00', 'Monday 2018-05-21 17:00'],
             ['Sunday 2018-05-20 16:00', 'Monday 2018-05-21 17:00'],
+            ['Friday 2019-06-28 00:00', 'Monday 2019-07-01 00:00'],
         ];
     }
 
@@ -108,8 +109,14 @@ public function addBusinessDaysProvider(): array
             ['Monday 2018-05-14 09:00', 1.5, 'Tuesday 2018-05-15 13:00'],
             ['Monday 2018-05-14 09:00', 1.75, 'Tuesday 2018-05-15 15:00'],
             ['Monday 2018-05-14 09:00', 2, 'Wednesday 2018-05-16 09:00'],
-            // From Friday evening.
+            // From Friday morning.
             ['Friday 2018-05-18 00:00', 0, 'Friday 2018-05-18 00:00'],
+            ['Friday 2018-05-18 00:00', 0.25, 'Friday 2018-05-18 11:00'],
+            ['Friday 2018-05-18 00:00', 0.5, 'Friday 2018-05-18 13:00'],
+            ['Friday 2018-05-18 00:00', 0.75, 'Friday 2018-05-18 15:00'],
+            ['Friday 2018-05-18 00:00', 1, 'Monday 2018-05-21 00:00'],
+            ['Friday 2018-05-18 00:00', 1.25, 'Monday 2018-05-21 11:00'],
+            // From Friday evening.
             ['Friday 2018-05-18 17:00', 0, 'Friday 2018-05-18 17:00'],
             ['Friday 2018-05-18 17:00', 0.25, 'Monday 2018-05-21 11:00'],
             ['Friday 2018-05-18 17:00', 0.5, 'Monday 2018-05-21 13:00'],
@@ -133,4 +140,19 @@ public function addBusinessDaysProvider(): array
             ['Friday 2018-05-18 17:00', -2, 'Wednesday 2018-05-16 17:00'],
         ];
     }
+
+    /**
+     * The addBusinessDay method should always return a business day.
+     */
+    public function testAlwaysEndsOnBusinessDay()
+    {
+        // Given we have a business time for Friday;
+        $businessTime = new BusinessTime('Friday');
+
+        // When we add one business day to it;
+        $addDay = $businessTime->addBusinessDay();
+
+        // Then it should be Monday.
+        self::assertEquals('Monday', $addDay->format('l'));
+    }
 }
diff --git a/tests/Unit/BusinessTime/SubBusinessDaysTest.php b/tests/Unit/BusinessTime/SubBusinessDaysTest.php
index e08c466..c460cca 100644
--- a/tests/Unit/BusinessTime/SubBusinessDaysTest.php
+++ b/tests/Unit/BusinessTime/SubBusinessDaysTest.php
@@ -58,6 +58,7 @@ public function subBusinessDayProvider(): array
             ['Monday 2018-05-21 13:00', 'Friday 2018-05-18 13:00'],
             ['Sunday 2018-05-20 11:00', 'Friday 2018-05-18 09:00'],
             ['Saturday 2018-05-19 10:00', 'Friday 2018-05-18 09:00'],
+            ['Monday 2018-05-21 17:00', 'Friday 2018-05-18 17:00'],
         ];
     }
 
@@ -114,6 +115,19 @@ public function subBusinessDaysProvider(): array
             ['Monday 2018-05-21 09:00', 1.5, 'Thursday 2018-05-17 13:00'],
             ['Monday 2018-05-21 09:00', 1.75, 'Thursday 2018-05-17 11:00'],
             ['Monday 2018-05-21 09:00', 2, 'Thursday 2018-05-17 09:00'],
+            // From Monday evening.
+            ['Monday 2018-05-21 17:00', 0, 'Monday 2018-05-21 17:00'],
+            ['Monday 2018-05-21 18:00', 0, 'Monday 2018-05-21 18:00'],
+            ['Monday 2018-05-21 18:00', 0.25, 'Monday 2018-05-21 15:00'],
+            ['Monday 2018-05-21 18:00', 0.5, 'Monday 2018-05-21 13:00'],
+            ['Monday 2018-05-21 18:00', 0.75, 'Monday 2018-05-21 11:00'],
+            ['Monday 2018-05-21 18:00', 1, 'Friday 2018-05-18 18:00'],
+            ['Monday 2018-05-21 18:00', 1.25, 'Friday 2018-05-18 15:00'],
+            ['Monday 2018-05-21 18:00', 1.5, 'Friday 2018-05-18 13:00'],
+            ['Monday 2018-05-21 18:00', 1.75, 'Friday 2018-05-18 11:00'],
+            ['Monday 2018-05-21 18:00', 2, 'Friday 2018-05-18 09:00'],
+            ['Monday 2018-05-21 18:00', 2.5, 'Thursday 2018-05-17 13:00'],
+            ['Monday 2018-05-21 18:00', 3, 'Thursday 2018-05-17 09:00'],
             // Negative values.
             ['Wednesday 2018-05-23 13:00', -0, 'Wednesday 2018-05-23 13:00'],
             ['Wednesday 2018-05-23 13:00', -0.25, 'Wednesday 2018-05-23 15:00'],
@@ -126,4 +140,19 @@ public function subBusinessDaysProvider(): array
             ['Wednesday 2018-05-23 13:00', -2, 'Friday 2018-05-25 13:00'],
         ];
     }
+
+    /**
+     * The subBusinessDay method should always return a business day.
+     */
+    public function testAlwaysEndsOnBusinessDay()
+    {
+        // Given we have a business time for Monday;
+        $businessTime = new BusinessTime('Monday');
+
+        // When we subtract one business day from it;
+        $addDay = $businessTime->subBusinessDay();
+
+        // Then it should be Friday.
+        self::assertEquals('Friday', $addDay->format('l'));
+    }
 }