diff --git a/src/codesnap/core/complexity.py b/src/codesnap/core/complexity.py
new file mode 100644
index 0000000..a823cca
--- /dev/null
+++ b/src/codesnap/core/complexity.py
@@ -0,0 +1,36 @@
+from __future__ import annotations
+
+import ast
+from codesnap.core.models import FunctionInfo
+
+
+class ComplexityCalculator:
+    def calculate_function_complexity(self, node: ast.FunctionDef | ast.AsyncFunctionDef, source: str) -> FunctionInfo:
+        lines = source.split("\n")
+        start_line = node.lineno
+        end_line = node.end_lineno or node.lineno
+
+        body = lines[start_line - 1 : end_line]
+        code = "\n".join(body)
+
+        complexity = 1
+        for child in ast.walk(node):
+            if isinstance(child, (ast.If, ast.For, ast.While, ast.Try, ast.With, ast.AsyncWith)):
+                complexity += 1
+            elif isinstance(child, ast.BoolOp):
+                complexity += len(child.values) - 1
+            elif isinstance(child, ast.comprehension):
+                complexity += 1
+
+        params = len(node.args.args)
+
+        docstring = ast.get_docstring(node)
+
+        return FunctionInfo(
+            name=node.name,
+            complexity=complexity,
+            parameters=params,
+            lines=end_line - start_line + 1,
+            code=code,
+            docstring=docstring,
+        )