diff --git a/src/converter.py b/src/converter.py
index 621039c..e10fb0c 100644
--- a/src/converter.py
+++ b/src/converter.py
@@ -72,17 +72,17 @@ class UnsupportedTargetFormatError(Exception):
     pass
 
 
-def convert(data: dict, target_format: str) -> str:
+def convert(data: dict, last_modified: datetime, target_format: str) -> str:
     match target_format:
         case "adguard":
-            return adguard_conversion(data)
+            return adguard_conversion(last_modified, data)
         case _:
             raise UnsupportedTargetFormatError
 
 
-def adguard_conversion(data: dict) -> list[str]:
+def adguard_conversion(last_modified: datetime, data: dict) -> list[str]:
     header_lines: list[str] = [
-        f"! Blocking list automatically generated at {datetime.now(timezone.utc).strftime('%Y-%m-%d %H:%M:%S %Z%z')}",
+        f"! Blocking list automatically generated at {last_modified.strftime('%Y-%m-%d %H:%M:%S %Z%z')}",
         "! Created with ❤️ by internet-czas-dzialac.pl",
     ]
 
@@ -107,6 +107,11 @@ def dump_output(data: str, output_file: str) -> None:
         file.write(data)
 
 
+def get_last_modified_datetime(file_path: str) -> datetime:
+    timestamp: float = os.path.getmtime(file_path)
+    return datetime.fromtimestamp(timestamp, tz=timezone.utc)
+
+
 def main() -> None:
     # Start measuring time
     start_time: float = perf_counter()
@@ -117,6 +122,7 @@ def main() -> None:
     # Load data
     try:
         data: dict = load_data(args.inputfile)
+        last_modified: datetime = get_last_modified_datetime(args.inputfile)
     except FileNotFoundError:
         logger.error(f"File {args.inputfile} not found!")
         return
@@ -129,7 +135,7 @@ def main() -> None:
 
     # Convert
     try:
-        output = convert(data, args.targetformat)
+        output = convert(data, last_modified, args.targetformat)
     except UnsupportedTargetFormatError:
         logger.error('Unsupported format. For now only "adguard" is supported.')
         return