Justin Bieber is given an allowance every month.

The 16-year-old singing sensation is worth an estimated $100 million but has a cap placed on his spending and is forced to go without if he reaches the top of his budget too soon.

He admitted: "My money is being invested. I only have a credit card, which allows me to spend a certain amount of money every month. If I reach the limit after the first week, I won't be able to buy any more stuff until the month is over. My mom is in control of that."

Despite the tight control placed on his finances, Justin insists he doesn't mind because he is more interested in his career than the financial rewards it brings.

He told Switzerland's Blick newspaper: "It's not that money wouldn't mean anything at all to me. But the main thing is to do what my passion is. And that's music. It's nice to get paid for that, though. Performing feels natural to me, just like walking."

As well as controlling his finances, the 'Baby' hitmaker's mother, Patti Mallette, also keeps a close eye on the fan mail the young star receives.

Asked about having underwear thrown at him on stage, he said: "My Mom doesn't like it when that happens. Sometimes they have phone numbers written on them. I don't know what happens to them."