With Affirm you pay once monthly for 3 months with 0% interest. You never pay more than what you agree to up front. To sign up for Affirm, you must: Be 18 years or older. Not be a resident of Iowa (IA) or West Virginia (WV). Provide a valid U.S. or APO/FPO/DPO home address. Provide a valid U.S. mobile or VoIP number and agree to receive SMS text messages. The phone account must be registered in your name. Provide your full name, email address, date of birth, and the last 4 digits of your social security number to help us verify your identity.