diff --git a/mft/routes/__init__.py b/mft/routes/__init__.py
index b558fd5..518316d 100644
--- a/mft/routes/__init__.py
+++ b/mft/routes/__init__.py
@@ -1,13 +1,9 @@
-"""API routes aggregation."""
-
 from fastapi import APIRouter
-
-from mft.routes import auth, categories, health
-
+from mft.routes import auth, categories, expense, health
 
 api_router = APIRouter()
 
-# Include all route modules
 api_router.include_router(health.router, tags=["health"])
 api_router.include_router(auth.router, prefix="/auth", tags=["auth"])
 api_router.include_router(categories.router, tags=["categories"])
+api_router.include_router(expense.router, tags=["expenses"])
diff --git a/mft/routes/auth.py b/mft/routes/auth.py
index 1a9b5dd..1a0961b 100644
--- a/mft/routes/auth.py
+++ b/mft/routes/auth.py
@@ -1,10 +1,6 @@
-"""Authentication routes."""
-
 from fastapi import APIRouter, Depends
-
 from mft.auth import verify_token
 
-
 router = APIRouter()
 
 
@@ -19,8 +15,4 @@ async def validate(user_id: int = Depends(verify_token)):
     Returns:
         A simple status response with the authenticated user ID
     """
-    return {
-        "status": "ok",
-        "user_id": user_id,
-        "message": "Successfully authenticated"
-    }
+    return {"status": "ok", "user_id": user_id, "message": "Successfully authenticated"}
diff --git a/mft/routes/categories.py b/mft/routes/categories.py
index 9e46813..0f5adc1 100644
--- a/mft/routes/categories.py
+++ b/mft/routes/categories.py
@@ -1,12 +1,8 @@
-"""Category endpoints."""
-
 from fastapi import APIRouter, Depends
 from pydantic import BaseModel
-
 from mft.auth import verify_token
 from mft.database import get_db
 
-
 router = APIRouter()
 
 
diff --git a/mft/routes/expense.py b/mft/routes/expense.py
new file mode 100644
index 0000000..c3ebf05
--- /dev/null
+++ b/mft/routes/expense.py
@@ -0,0 +1,68 @@
+import sqlite3
+from datetime import datetime, timezone
+from fastapi import APIRouter, HTTPException, status, Depends
+from pydantic import BaseModel, Field
+from mft.auth import verify_token
+from mft.database import get_db
+
+router = APIRouter()
+
+
+class ExpenseCreate(BaseModel):
+    cid: int = Field(..., description="Category ID")
+    value: int = Field(..., gt=0, description="Amount in cents")
+    note: str | None = Field(None, description="Optional note")
+
+
+class Expense(BaseModel):
+    id: int
+    uid: int
+    cid: int
+    ts: str
+    value: int
+    note: str | None
+
+
+@router.post("/expenses", response_model=Expense, status_code=status.HTTP_201_CREATED)
+def create_expense(expense: ExpenseCreate, uid: int = Depends(verify_token)):
+    """
+    Create a new expense entry.
+
+    Args:
+        expense: Expense data (category ID, value in cents, optional note)
+        uid: User ID from authentication token
+
+    Returns:
+        The created expense with generated ID and timestamp
+
+    Raises:
+        400: Invalid category ID or constraint violation
+    """
+    timestamp = datetime.now(timezone.utc).isoformat()
+
+    with get_db() as conn:
+        cursor = conn.cursor()
+        try:
+            cursor.execute(
+                """
+                INSERT INTO expense (uid, cid, ts, value, note)
+                VALUES (?, ?, ?, ?, ?)
+                """,
+                (uid, expense.cid, timestamp, expense.value, expense.note),
+            )
+            conn.commit()
+            expense_id = cursor.lastrowid
+
+            return Expense(
+                id=expense_id,
+                uid=uid,
+                cid=expense.cid,
+                ts=timestamp,
+                value=expense.value,
+                note=expense.note,
+            )
+        except sqlite3.IntegrityError as e:
+            raise HTTPException(
+                status_code=status.HTTP_400_BAD_REQUEST,
+                detail="Invalid request: constraint violation",
+            ) from e
diff --git a/mft/routes/health.py b/mft/routes/health.py
index 8349c6a..f8187bd 100644
--- a/mft/routes/health.py
+++ b/mft/routes/health.py
@@ -1,12 +1,8 @@
-"""Health check and status endpoints."""
-
 from fastapi import APIRouter
 
-
 router = APIRouter()
 
 
 @router.get("/status")
 async def status():
-    """Minimal status check to verify the API is up."""
     return {"status": "ok"}