When will I receive my membership number? Thank you for joining and welcome to Alliant! If you applied for membership through the Alliant Online Banking system, your membership number is automatically generated and visible on your online account homepage for 30 days after your application is approved. You can always find your membership number in your Account Details folder online. Your Alliant Welcome Package, which will arrive by mail within 7-10 days after you’re application has been approved, also contains your membership number.