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 extends by 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? How can you add credit to your account? Why can't you see your credit after you Top Up? What is your bonus credit?