What is the airtime for a prepaid top-up? Sim airtime is the total number of days you get each time credit is applied to your account. With every top up, your airtime resets to 120 days. You can dial *120# to check your airtime status. Related articles How can you check your balance? How much am I paying to make calls? What is your bonus credit? How to top up with a voucher card Why can't you see your credit after you Top Up?