diff --git a/web/src/padelnomics/core.py b/web/src/padelnomics/core.py
index 5260ec0..c762d5f 100644
--- a/web/src/padelnomics/core.py
+++ b/web/src/padelnomics/core.py
@@ -10,7 +10,7 @@ import re
 import secrets
 import unicodedata
 from contextvars import ContextVar
-from datetime import datetime, timedelta
+from datetime import UTC, datetime, timedelta
 from functools import wraps
 from pathlib import Path
 
@@ -88,6 +88,26 @@ class Config:
 
 config = Config()
 
+
+# =============================================================================
+# Datetime helpers
+# =============================================================================
+
+
+def utcnow() -> datetime:
+    """Timezone-aware UTC now (replaces deprecated datetime.utcnow())."""
+    return datetime.now(UTC)
+
+
+def utcnow_iso() -> str:
+    """UTC now as naive ISO string for SQLite TEXT columns.
+
+    Produces YYYY-MM-DDTHH:MM:SS (no +00:00 suffix) to match the existing
+    format stored in the DB so lexicographic SQL comparisons keep working.
+    """
+    return datetime.now(UTC).strftime("%Y-%m-%dT%H:%M:%S")
+
+
 # =============================================================================
 # Database
 # =============================================================================
@@ -528,17 +548,18 @@ async def check_rate_limit(key: str, limit: int = None, window: int = None) -> t
     """
     limit = limit or config.RATE_LIMIT_REQUESTS
     window = window or config.RATE_LIMIT_WINDOW
-    now = datetime.utcnow()
+    now = utcnow()
     window_start = now - timedelta(seconds=window)
 
     # Clean old entries and count recent
     await execute(
-        "DELETE FROM rate_limits WHERE key = ? AND timestamp < ?", (key, window_start.isoformat())
+        "DELETE FROM rate_limits WHERE key = ? AND timestamp < ?",
+        (key, window_start.strftime("%Y-%m-%dT%H:%M:%S")),
     )
 
     result = await fetch_one(
         "SELECT COUNT(*) as count FROM rate_limits WHERE key = ? AND timestamp > ?",
-        (key, window_start.isoformat()),
+        (key, window_start.strftime("%Y-%m-%dT%H:%M:%S")),
     )
     count = result["count"] if result else 0
 
@@ -552,7 +573,10 @@ async def check_rate_limit(key: str, limit: int = None, window: int = None) -> t
         return False, info
 
     # Record this request
-    await execute("INSERT INTO rate_limits (key, timestamp) VALUES (?, ?)", (key, now.isoformat()))
+    await execute(
+        "INSERT INTO rate_limits (key, timestamp) VALUES (?, ?)",
+        (key, now.strftime("%Y-%m-%dT%H:%M:%S")),
+    )
 
     return True, info
 
@@ -628,7 +652,7 @@ async def soft_delete(table: str, id: int) -> bool:
     """Mark record as deleted."""
     result = await execute(
         f"UPDATE {table} SET deleted_at = ? WHERE id = ? AND deleted_at IS NULL",
-        (datetime.utcnow().isoformat(), id),
+        (utcnow_iso(), id),
     )
     return result > 0
 
@@ -647,7 +671,7 @@ async def hard_delete(table: str, id: int) -> bool:
 
 async def purge_deleted(table: str, days: int = 30) -> int:
     """Purge records deleted more than X days ago."""
-    cutoff = (datetime.utcnow() - timedelta(days=days)).isoformat()
+    cutoff = (utcnow() - timedelta(days=days)).strftime("%Y-%m-%dT%H:%M:%S")
     return await execute(
         f"DELETE FROM {table} WHERE deleted_at IS NOT NULL AND deleted_at < ?", (cutoff,)
     )