Female singers dominated the top of Forbes' list of the highest-paid celebrities under the age of 30, released Thursday, starting with country pop sensation Taylor Swift. The business magazine said the 22-year-old Swift earned US$57 million in the 12 months to May, a period that included the North American and Australasian legs of her 111-concert "Speak Now" tour. Forbes said each Swift concert raked in an average of US$1 million, with multi-platinum album sales and product endorsements topping up her wealth. She is expected to release a new album in October. Teen idol Justin Bieber, 18, the only male in the top five, placed second at US$55 million, followed by Rihanna (US$53 million), Lady Gaga (US$52 million) and Katy Perry (US$45 million). Last year, Lady Gaga topped the list at US$90 million. Forbes said her slump is likely due to the fact that she did not tour during its May-to-May review period. "Expect the pop princess to earn more next year," it said. Forbes said it considered "album and concert sales, movie paydays, profit participation, endorsements and advertising work," and interviewed showbiz insiders such as managers and agents, in coming up with its under-30 list. It did not deduct agent fees -- typically double-digit -- or what it called "expenses related to being a celebrity."