O2 is one of the four UK mobile network operators (MNOs), so its Pay As You Go customers are buying directly from the network rather than from an MVNO that resells O2 capacity. The trade-off is that O2 PAYG can be a little pricier than its MVNO siblings on the same masts (giffgaff and Tesco Mobile both run on O2), but you get O2's full coverage, retail support and access to O2 Priority - the customer rewards programme that gives priority access to gig tickets and weekly perks across high-street brands. Topping up your O2 PAYG SIM is simple, and there are five ways to do it: online, in the My O2 app, with a top-up voucher from a UK retailer, in person at an O2 store or partner shop, or by setting up auto top-up so you never run out of credit.
Once you have credit, you can either keep it as flexible PAYG to pay per minute, text and MB at standard PAYG rates, or convert it into a Big Bundle, which is O2's name for the 30-day allowance packs that include data, calls and texts. Big Bundles are far better value than spending credit on standard PAYG rates if you use your phone regularly, and most include 5G access on supported phones at no extra cost. Credit on O2 PAYG lasts 6 months from your last top-up, so a small top-up twice a year keeps the SIM and number active even if you barely use the phone.
If you top up the same amount every month, switching to a SIM-only contract normally saves money for the same allowances - 30-day rolling SIMs from O2 and other UK networks usually undercut PAYG by a few pounds a month. You can keep your existing number when you switch by getting a free PAC code from O2 first. This guide covers every top-up option, current Big Bundle pricing, voucher locations and the most common questions O2 PAYG customers have.
Topping up the same amount every month?
If you reliably buy a Big Bundle every month, a 30-day SIM-only plan from O2 or another UK network usually costs less for the same allowances. Compare rolling SIM-only plans across EE, O2, Three, Vodafone and the biggest MVNOs.
