diff --git a/src/Personnummer.php b/src/Personnummer.php
index 1d28d32..015001b 100644
--- a/src/Personnummer.php
+++ b/src/Personnummer.php
@@ -25,6 +25,8 @@ final class Personnummer implements PersonnummerInterface
 
     private array $options;
 
+    private bool $isInterim;
+
     /**
      * @inheritDoc
      */
@@ -88,6 +90,14 @@ public function isCoordinationNumber(): bool
         return checkdate((int)$parts['month'], $parts['day'] - 60, $parts['fullYear']);
     }
 
+    /**
+     * @inheritDoc
+     */
+    public function isInterimNumber(): bool
+    {
+        return $this->isInterim;
+    }
+
     /**
      * @inheritDoc
      */
@@ -256,9 +266,9 @@ private function isValid(): bool
 
         // Correct interim if allowed.
         $interimTest = '/(?![-+])\D/';
-        $isInterim = preg_match($interimTest, $parts['original']) !== 0;
+        $this->isInterim = preg_match($interimTest, $parts['original']) !== 0;
 
-        if ($this->options['allowInterimNumber'] === false && $isInterim) {
+        if ($this->options['allowInterimNumber'] === false && $this->isInterim) {
             throw new PersonnummerException(sprintf(
                 '%s contains non-integer characters and options are set to not allow interim numbers',
                 $parts['original']
@@ -266,7 +276,7 @@ private function isValid(): bool
         }
 
         $num = $parts['num'];
-        if ($this->options['allowInterimNumber'] && $isInterim) {
+        if ($this->options['allowInterimNumber'] && $this->isInterim) {
             $num = preg_replace($interimTest, '1', $num);
         }
 
diff --git a/src/PersonnummerInterface.php b/src/PersonnummerInterface.php
index c41a3d6..cc87151 100644
--- a/src/PersonnummerInterface.php
+++ b/src/PersonnummerInterface.php
@@ -72,6 +72,13 @@ public function isMale(): bool;
      */
     public function isCoordinationNumber(): bool;
 
+    /**
+     * Check if the Swedish social security number is an interim number.
+     *
+     * @return bool
+     */
+    public function isInterimNumber(): bool;
+
     public function __construct(string $ssn, array $options = []);
 
     /**
diff --git a/tests/InterimNumberTest.php b/tests/InterimNumberTest.php
index 9da74db..b1489f5 100644
--- a/tests/InterimNumberTest.php
+++ b/tests/InterimNumberTest.php
@@ -60,6 +60,13 @@ public function testValidateInvalidInterim(PersonnummerData $num): void
         self::assertFalse(Personnummer::valid($num->separatedFormat, $this->options));
     }
 
+    #[DataProvider('validProvider')]
+    public function testIsInterim(PersonnummerData $num): void
+    {
+        self::assertTrue(Personnummer::parse($num->longFormat, $this->options)->isInterimNumber());
+        self::assertTrue(Personnummer::parse($num->separatedFormat, $this->options)->isInterimNumber());
+    }
+
     #[DataProvider('validProvider')]
     public function testFormatLongInterim(PersonnummerData $num): void
     {
diff --git a/tests/PersonnummerData.php b/tests/PersonnummerData.php
index a00b0f1..5f3f79e 100644
--- a/tests/PersonnummerData.php
+++ b/tests/PersonnummerData.php
@@ -1,4 +1,5 @@
 <?php
+
 namespace Personnummer\Tests;
 
 class PersonnummerData
@@ -14,7 +15,6 @@ public function __construct(array $p)
         $this->isMale = $p['isMale'];
         $this->isFemale = $p['isFemale'];
     }
-
     public string $longFormat;
     public string $shortFormat;
     public string $separatedFormat;
diff --git a/tests/PersonnummerTest.php b/tests/PersonnummerTest.php
index 29fcba3..a9824e8 100644
--- a/tests/PersonnummerTest.php
+++ b/tests/PersonnummerTest.php
@@ -227,4 +227,13 @@ public function testMissingProperties(): void
         }, E_USER_NOTICE);
         $this->assertFalse(isset(Personnummer::parse('121212-1212')->missingProperty));
     }
+
+    public function testIsNotInterim(): void
+    {
+        foreach (self::$testdataList as $testdata) {
+            if ($testdata['valid']) {
+                $this->assertFalse(Personnummer::parse($testdata['separated_format'])->isInterimNumber());
+            }
+        }
+    }
 }