diff --git a/backend/CLAUDE.md b/backend/CLAUDE.md
index 414c4c70..8ab0a12c 100644
--- a/backend/CLAUDE.md
+++ b/backend/CLAUDE.md
@@ -473,6 +473,15 @@ python manage.py shell
 # Run tests
 python manage.py test
 
+# Preview stale SIWE nonce cleanup
+python manage.py cleanup_nonces --dry-run
+
+# Delete nonces expired more than 1 hour ago and used nonces created more than 1 hour ago
+python manage.py cleanup_nonces
+
+# Use a custom cleanup threshold, in hours
+python manage.py cleanup_nonces --hours 24
+
 # Collect static files
 python manage.py collectstatic
 ```
diff --git a/backend/ethereum_auth/management/__init__.py b/backend/ethereum_auth/management/__init__.py
new file mode 100644
index 00000000..e69de29b
diff --git a/backend/ethereum_auth/management/commands/__init__.py b/backend/ethereum_auth/management/commands/__init__.py
new file mode 100644
index 00000000..e69de29b
diff --git a/backend/ethereum_auth/management/commands/cleanup_nonces.py b/backend/ethereum_auth/management/commands/cleanup_nonces.py
new file mode 100644
index 00000000..c1ebb25e
--- /dev/null
+++ b/backend/ethereum_auth/management/commands/cleanup_nonces.py
@@ -0,0 +1,56 @@
+import math
+from datetime import timedelta
+
+from django.core.management.base import BaseCommand, CommandError
+from django.db.models import Q
+from django.utils import timezone
+
+from ethereum_auth.models import Nonce
+
+
+class Command(BaseCommand):
+    help = 'Remove expired SIWE nonces and used SIWE nonces older than the cleanup threshold.'
+
+    def add_arguments(self, parser):
+        parser.add_argument(
+            '--hours',
+            type=float,
+            default=1,
+            help=(
+                'Delete nonces expired more than this many hours ago and used '
+                'nonces created more than this many hours ago (default: 1).'
+            ),
+        )
+        parser.add_argument(
+            '--dry-run',
+            action='store_true',
+            help='Show how many nonces would be deleted without removing them.',
+        )
+
+    def handle(self, *args, **options):
+        hours = options['hours']
+        if not math.isfinite(hours) or hours < 0:
+            raise CommandError('--hours must be a finite number greater than or equal to 0')
+
+        try:
+            cutoff = timezone.now() - timedelta(hours=hours)
+        except OverflowError as exc:
+            raise CommandError('--hours is too large') from exc
+
+        stale_nonces = Nonce.objects.filter(
+            Q(expires_at__lte=cutoff) | Q(used=True, created_at__lte=cutoff)
+        )
+        count = stale_nonces.count()
+
+        if options['dry_run']:
+            self.stdout.write(
+                self.style.WARNING(
+                    f'Dry run: {count} stale nonce(s) would be deleted.'
+                )
+            )
+            return
+
+        deleted_count, _ = stale_nonces.delete()
+        self.stdout.write(
+            self.style.SUCCESS(f'Deleted {deleted_count} stale nonce(s).')
+        )
diff --git a/backend/ethereum_auth/tests.py b/backend/ethereum_auth/tests.py
index 87586fc5..0928d886 100644
--- a/backend/ethereum_auth/tests.py
+++ b/backend/ethereum_auth/tests.py
@@ -1,4 +1,8 @@
+from io import StringIO
+
 from django.contrib.auth import get_user_model
+from django.core.management import call_command
+from django.core.management.base import CommandError
 from django.test import TestCase, override_settings
 from django.utils import timezone
 from eth_account import Account
@@ -162,3 +166,68 @@ def test_login_rejects_recovery_message_shape(self):
         self.assertEqual(response.status_code, 400)
         nonce.refresh_from_db()
         self.assertFalse(nonce.used)
+
+
+class CleanupNoncesCommandTests(TestCase):
+    def _nonce(self, value, *, used=False, expires_delta=None, created_delta=None):
+        now = timezone.now()
+        return Nonce.objects.create(
+            value=value,
+            used=used,
+            created_at=now + (created_delta or timezone.timedelta()),
+            expires_at=now + expires_delta,
+        )
+
+    def test_cleanup_nonces_deletes_only_stale_used_or_expired_nonces(self):
+        old_expired = self._nonce(
+            'oldExpiredNonce',
+            expires_delta=timezone.timedelta(hours=-3),
+        )
+        old_used = self._nonce(
+            'oldUsedNonce',
+            used=True,
+            created_delta=timezone.timedelta(hours=-2),
+            expires_delta=timezone.timedelta(minutes=5),
+        )
+        recent_expired = self._nonce(
+            'recentExpiredNonce',
+            expires_delta=timezone.timedelta(minutes=-15),
+        )
+        recent_used = self._nonce(
+            'recentUsedNonce',
+            used=True,
+            created_delta=timezone.timedelta(minutes=-15),
+            expires_delta=timezone.timedelta(minutes=5),
+        )
+        active = self._nonce(
+            'activeNonce',
+            expires_delta=timezone.timedelta(minutes=5),
+        )
+
+        output = StringIO()
+        call_command('cleanup_nonces', hours=1, stdout=output)
+
+        self.assertIn('Deleted 2 stale nonce(s).', output.getvalue())
+        self.assertFalse(Nonce.objects.filter(pk=old_expired.pk).exists())
+        self.assertFalse(Nonce.objects.filter(pk=old_used.pk).exists())
+        self.assertTrue(Nonce.objects.filter(pk=recent_expired.pk).exists())
+        self.assertTrue(Nonce.objects.filter(pk=recent_used.pk).exists())
+        self.assertTrue(Nonce.objects.filter(pk=active.pk).exists())
+
+    def test_cleanup_nonces_dry_run_reports_without_deleting(self):
+        old_expired = self._nonce(
+            'dryRunExpiredNonce',
+            expires_delta=timezone.timedelta(hours=-3),
+        )
+
+        output = StringIO()
+        call_command('cleanup_nonces', hours=1, dry_run=True, stdout=output)
+
+        self.assertIn('Dry run: 1 stale nonce(s) would be deleted.', output.getvalue())
+        self.assertTrue(Nonce.objects.filter(pk=old_expired.pk).exists())
+
+    def test_cleanup_nonces_rejects_invalid_retention_window(self):
+        for invalid_hours in (-1, float('nan'), float('inf'), float('-inf'), 1e20):
+            with self.subTest(hours=invalid_hours):
+                with self.assertRaises(CommandError):
+                    call_command('cleanup_nonces', hours=invalid_hours)