diff --git a/eeg_backend/src/main/java/at/mueller/eeg/backend/iam/domain/User.java b/eeg_backend/src/main/java/at/mueller/eeg/backend/iam/domain/User.java
index 2853618..bb7bbff 100644
--- a/eeg_backend/src/main/java/at/mueller/eeg/backend/iam/domain/User.java
+++ b/eeg_backend/src/main/java/at/mueller/eeg/backend/iam/domain/User.java
@@ -65,6 +65,13 @@ public class User implements UserDetails {
     @Column(nullable = false)
     private boolean enabled = false;
 
+    @PrePersist
+    protected void onCreate() {
+        if (createdAt == null) {
+            createdAt = LocalDateTime.now();
+        }
+    }
+
     @Override
     @NonNull
     public Collection<? extends GrantedAuthority> getAuthorities() {
diff --git a/eeg_backend/src/test/java/at/mueller/eeg/backend/iam/domain/UserTest.java b/eeg_backend/src/test/java/at/mueller/eeg/backend/iam/domain/UserTest.java
index e0d0c03..453e404 100644
--- a/eeg_backend/src/test/java/at/mueller/eeg/backend/iam/domain/UserTest.java
+++ b/eeg_backend/src/test/java/at/mueller/eeg/backend/iam/domain/UserTest.java
@@ -33,4 +33,28 @@ class UserTest {
 
         assertNull(user.getCreatedAt(), "createdAt should default to null (not auto-generated)");
     }
+
+    @Test
+    void prePersistSetsCreatedAt() {
+        User user = new User();
+
+        LocalDateTime before = LocalDateTime.now();
+        user.onCreate();
+        LocalDateTime after = LocalDateTime.now();
+
+        assertNotNull(user.getCreatedAt(), "createdAt must be set by @PrePersist callback");
+        assertFalse(user.getCreatedAt().isBefore(before), "createdAt must not be before test start");
+        assertFalse(user.getCreatedAt().isAfter(after), "createdAt must not be after test end");
+    }
+
+    @Test
+    void prePersistDoesNotOverwriteExistingCreatedAt() {
+        User user = new User();
+        LocalDateTime fixed = LocalDateTime.of(2025, 1, 1, 12, 0);
+        user.setCreatedAt(fixed);
+
+        user.onCreate();
+
+        assertEquals(fixed, user.getCreatedAt(), "createdAt must not be overwritten if already set");
+    }
 }