diff --git a/filter/kyofilter b/filter/kyofilter
index 92228b2..545bf4a 100755
--- a/filter/kyofilter
+++ b/filter/kyofilter
@@ -14,5 +14,15 @@ def parse_options(options_str):
     return options
 
 
+def get_account_code(options):
+    km = options.get('KmManagment', 'Default')
+    if km == 'Default' or not km.startswith('MG'):
+        return None
+    code = km[2:]
+    if not code.isdigit():
+        return None
+    return code.zfill(8)
+
+
 if __name__ == '__main__':
     pass
diff --git a/tests/test_kyofilter.py b/tests/test_kyofilter.py
index 9bf95f7..df1727e 100644
--- a/tests/test_kyofilter.py
+++ b/tests/test_kyofilter.py
@@ -14,3 +14,26 @@ class TestParseOptions:
 
     def test_flag_without_value(self):
         assert kyofilter.parse_options("SomeFlag") == {"SomeFlag": "true"}
+
+
+class TestGetAccountCode:
+    def test_five_digit_code_zero_padded_to_eight(self):
+        assert kyofilter.get_account_code({"KmManagment": "MG12345"}) == "00012345"
+
+    def test_one_digit_code_zero_padded(self):
+        assert kyofilter.get_account_code({"KmManagment": "MG1"}) == "00000001"
+
+    def test_eight_digit_code_unchanged(self):
+        assert kyofilter.get_account_code({"KmManagment": "MG12345678"}) == "12345678"
+
+    def test_default_returns_none(self):
+        assert kyofilter.get_account_code({"KmManagment": "Default"}) is None
+
+    def test_missing_key_returns_none(self):
+        assert kyofilter.get_account_code({}) is None
+
+    def test_no_mg_prefix_returns_none(self):
+        assert kyofilter.get_account_code({"KmManagment": "12345"}) is None
+
+    def test_non_numeric_code_returns_none(self):
+        assert kyofilter.get_account_code({"KmManagment": "MGabc45"}) is None