diff --git a/backend/api/routes/calc.py b/backend/api/routes/calc.py
index edf6b435..cbbaf704 100644
--- a/backend/api/routes/calc.py
+++ b/backend/api/routes/calc.py
@@ -2,7 +2,7 @@ from api.core.Gzip import register_gzip_request
 from fastapi import APIRouter, Body
 from api.core.Response import response
 from api.dp import AltersDep
-from core.basic.character import createCharacter
+from services.calc_service import calculate
 
 router = APIRouter()
 
@@ -11,5 +11,4 @@ register_gzip_request(router)
 
 @router.post('/calc')
 async def calc(state: AltersDep, config=Body(None)):
-    character = createCharacter(state.alter, state.equVersion)
-    return response(data=character.calc(config))
+    return response(data=calculate(state, config))
diff --git a/backend/services/__init__.py b/backend/services/__init__.py
new file mode 100644
index 00000000..d022bef7
--- /dev/null
+++ b/backend/services/__init__.py
@@ -0,0 +1 @@
+"""Application services for backend API orchestration."""
diff --git a/backend/services/calc_service.py b/backend/services/calc_service.py
new file mode 100644
index 00000000..1ea3ec08
--- /dev/null
+++ b/backend/services/calc_service.py
@@ -0,0 +1,10 @@
+from typing import Any
+
+from api.core.Auth import AlterState
+from core.basic.character import createCharacter
+
+
+def calculate(state: AlterState, config: dict[str, Any] | None) -> dict[str, Any]:
+    safe_config = config or {}
+    character = createCharacter(state.alter, state.equVersion)
+    return character.calc(safe_config)
diff --git a/backend/tests/unit/test_calc_service.py b/backend/tests/unit/test_calc_service.py
new file mode 100644
index 00000000..df3254fd
--- /dev/null
+++ b/backend/tests/unit/test_calc_service.py
@@ -0,0 +1,11 @@
+from api.core.Auth import AlterState
+from services.calc_service import calculate
+
+
+def test_calculate_returns_character_calc_result(minimal_calc_config):
+    state = AlterState('GF.swordman_male.weapon_master', 'token', {}, '0', 0)
+
+    result = calculate(state, minimal_calc_config)
+
+    assert isinstance(result, dict)
+    assert set(['uuid', 'skills', 'info', 'suits', 'buffer']).issubset(result)