Roaming charges and international calls are amongst the two biggest causes
UK Mobile users are forking out close to £500 million each year on unexpected bill charges according to Uswitch.
The price comparison and switching service revealed that UK users pay £489 million on unexpected costs, with many not checking their bills thoroughly.
In the past year a third of Brits (32 per cent) paid additional unexpected costs.
During this time, those affected paid close to £40 (£38.90) in extra costs, in the past 12 months.
The most common reasons for the unexpected costs are roaming charges, international costs, in-game currencies, app purchases and app subscriptions.
Almost half (47pc) of the 2,000 people surveyed by Uswitch’s study admitted to not checking their bill every month.
A fifth of people admitted to never checking their bills, while parents often blamed their children for their surprise charges.
Uswitch estimates that children are responsible for adding £60 million to their parents mobile bills across the UK each year, mainly through in-app purchases.
Uswitch.com telecoms expert Ru Bhikha said: “At a time when millions of Britons are watching what they spend in other areas, it’s a surprise that so many are taking their eye off the ball when it comes to their phone.
“Keeping on top of your mobile costs is a good place to start when watching your pennies, and you should get into the habit of checking your bill every month.”