A combined net worth of $78.5 billion
Each year, Forbes crunches the net worth of every American billionaire to see who will make the exclusive Forbes 400 list. But 11 members of this club are luckier than the rest: they are in good health, have full heads of hair and many, many years to spend their fortunes.

This year there are 11 American billionaires under the age of 40 on the list. The youngest member of the Forbes 400 is 30-year-old Facebook cofounder Dustin Moskovitz, who has been the most junior person on the Forbes 400 since making his debut in 2010. He lost bragging rights as country’s youngest billionaire this summer when Snapchat raised money valuing the photo sharing app at $10 billion. Now Evan Spiegel, 24, holds that title but with a net worth of $1.5 billion, he just misses the cut for the Forbes 400.

Moskovitz is just eight days younger than his former Harvard roommate, Mark Zuckerberg, who is the second-most-junior member of the list. The Facebook CEO is worth an estimated $34 billion, up from $19 billion last year, making him the year’s biggest dollar gainer. At just 30 years old, he is the 11th richest person in America – and the wealthiest under 40.

A close third is newcomer Elizabeth Holmes, also 30 but born in February, who joins the ranking this year thanks to her blood testing company Theranos. Holmes founded the Palo Alto, Calif.-based company with money saved for college, and has reportedly raised more than $400 million, valuing the 10-year-old company at $9 billion . Two other new additions to the Forbes 400 who fall into the under 40 club are WhatsApp’s Jan Koum, who, aged 38, is worth $7.6 billion, and Uber cofounder Travis Kalanick, also 38, who joins with a $3 billion fortune thanks to his ride-sharing company.

Unsurprisingly, Silicon Valley whiz kids dominate the billionaire nursery. Napster cofounder and former Facebook CEO Sean Parker is 34, while Twitter cofounder and Square CEO Jack Dorsey is 37. Wireless network entrepreneur and Memphis Grizzlies owner Robert Pera, 36, ranks with a $2.8 billion fortune founded on his Ubiquiti Networks while GoPro camera maker’s Nick Woodman, 39, is worth an estimated $3.9 billion. In percentage terms,Woodman is the year’s biggest gainer, with a 200% increase in his net worth since last year, to $3.9 billion. GoPro went public in June; the stock has been soaring as more people buy GoPro cameras and strap them onto bike helmets, surfboards, scuba gear and more.

Outside of tech, there are still fortunes to be made – or inherited. Scott Duncan, worth $7 billion aged 31, is one of four billionaire siblings who are heirs to the energy-pipeline fortune built by their late father, Dan Duncan. While hedge fund managers have previously had a strong showing in the freshman class of the Forbes 400, this year only Chase Coleman, 39, makes the cut. His Tiger Global Management has about $12 billion in assets under management; Coleman’s personal fortune nears $1.9 billion.

This year’s group of 11 youngest billionaires in America have a combined net worth of $78.5 billion, or just under 4% of the $2.29 trillion aggregate net worth of the Forbes 400 ranking.

1 ) Dustin Moskovitz

Age: 30

Net worth: $8.1 billion

Mark Zuckerberg’s roommate at Harvard and Facebook’s third employee, Dustin Moskovitz left the social network in 2008 to start software firm Asana. He and his wife, a former Wall Street Journal reporter, devote some time to their Good Ventures, which has given millions to such causes as malaria eradication and marriage equality. Moskovitz bikes to work and flies commercial. He is also a regular attendee at Burning M

2 ) Mark Zuckerberg
Age: 30

Net worth: $34 billion

Facebook founder and CEO Mark Zuckerberg swung big in the past year to keep his social network from eventually becoming irrelevant. In February Facebook shocked the tech world, snapping up mobile messaging app WhatsApp for $19 billion in cash and stock. The following month it announced a $2 billion acquisition of virtual reality headset maker Oculus VR. Facebook stock has soared, adding $15 billion to Zuck’s net worth over the past year, making him the biggest gainer on the list in dollars terms.

3 ) Elizabeth Holmes
Age: 30

Net worth: $4.5 billion

At 30, Elizabeth Holmes makes her debut on the Forbes 400 as the youngest self-made woman billionaire. She dropped out her sophomore year of Stanford University to found Palo Alto, Calif.-based blood testing company Theranos in 2003 with money she saved for college. With a painless prick, her labs can quickly test a drop of blood at a fraction of the price of commercial labs which need more than one vial. Theranos has raised $400 million from venture capitalists, valuing the company at $9 billion, and Holmes’ 50% stake at $4.5 billion. She has assembled a stellar board that includes elder statesmen George Shultz and Henry Kissinger. Last year, Walgreens, the largest U.S. retail pharmacy chain, with more than 8,100 stores, announced plans to roll out Theranos Wellness Centers inside its pharmacies.

4 ) Scott Duncan
Net worth: $7 billion

Scott Duncan is America’s youngest billionaire to have inherited his wealth — setting him apart from the tech junkies who also make the list of 30-somethings in the .1%. He is the youngest of four siblings who are heirs to their late father Dan Duncan’s energy pipeline empire. Duncan, formerly the richest man in Houston, died in 2010 at age 77. Enterprise Products Partners has seen its stock surge since last year, building off high demand for natural gas, oil and petrochemical pipelines. It now owns nearly 51,000 miles of pipeline. His net worth has climbed $1 billion since last year due to generous dividend payouts and the quickly growing stock. His sister Randa Duncan Williams is the non-executive Chairman of the board. His two other siblings, Dannine Avara and Milane Frantz, are also billionaires.

5 ) Sean Parker
Age: 34

Net worth: $3 billion

The Napster cofounder and founding Facebook president has turned his attention to politics. In April, he started Brigade Media, a startup that will harness technology to enhance civic engagement. He contributed most of the venture’s $9.3 million in early funding, with angel investor Ron Conway and Salesforce.com founder Marc Benioff chipping in. Parker has given more than $1.4 million to political candidates since last year. For reasons he hasn’t explained, he ramped up his contributions to Republicans, after donating mostly to Democrats in the past. Parker’s fortune reached the $3 billion mark this year thanks to rising share prices for Facebook. Parker is no longer making new investments with Founders Fund, Peter Thiel’s venture firm, which he joined after leaving Facebook in 2006. He’s still a partner in earlier funds and remains on Spotify’s board. He’s also quietly re-launching Airtime, a video chat start-up that flopped two years ago, under a different name.

6 ) Robert Pera
Age: 36

Net worth: $2.8 billion

Robert Pera started as a hardware engineer at Apple in 2003 but bolted exactly two years later to start his own tech company, Ubiquiti Networks. He later said “Apple is a great company, but I realized I wanted to have more success faster.” Ubiquiti, a software and systems communications technology company focused on emerging markets, keeps costs low to out compete established competitors like Motorola on price while maintaining robust profit margins. Ubiquiti’s product range includes Wi-Fi amplification systems that can provide internet access to as few as 10 people or more than 10,000 customers within a 36-mile radius. He took the company public in October 2011, turning him into a billionaire at 34; stock tanked the next year amid Wall Street skepticism and a problem with a Chinese distributor which Ubiquiti sued for counterfiting the company’s products. A Shenzen court, with help from Ubiquiti, recently sentenced one of the distributor’s leaders to five years in prison. Three years after purchasing a 25% stake in the NBA’S Memphis Grizzilies Pera is taking on a bigger role in the team’s management.

7 ) Jack Dorsey
Age: 37

Net worth: $2.7 billion

Jack Dorsey counts with all of the characteristics that make a Silicon Valley visionary: he dropped out of college, founded one of the most popular, and valuable, social networks around, and was again ahead of the curve adopting new technology with mobile payments and wallets. Jack Dorsey co-founded Twitter with Ev Williams, Biz Stone, and Noah Glass in 2006, and still derives the bulk of his fortune from his ownership in the company, which stands around 4%. Having moved out of the CEO seat in 2008, he’s Twitter’s current chairman. His attention, though, is focused on Square, the mobile payments app he founded and leads that broke open the market through its innovative reader, which turned every smartphone into a credit card processing machine. As rivals have ramped up the competition, Square has suffered, though, with reports of 2013 losses in the $100 million range and drying cash reserves. Transactions in secondary markets put the company’s value at $5 billion, as Dorsey managed to secure additional financing from a consortium of Wall Street banks including Goldman Sachs and JPMorgan Chase. A certified masseur, Dorsey dropped out of NYU in 1999 and used to frequent punk concerts in his youth. The tattooed entrepreneur has evolved through the years, growing a beard and expressing his interest in becoming New York City Mayor at some point. Dorsey’s father worked for a company that developed mass spectrometers, while his mother was a homemaker.

8 ) Jan Koum
Age: 38

Net worth: $7.6 billion

Born in the Ukraine, Jan Koum and his mother immigrated to California when he was 16 and got an apartment through government assistance. She babysat, he swept floors to make ends meet. When she was diagnosed with cancer, they lived off her disability. He had a knack for computers and got a job working at Yahoo as a security and infrastructure engineer for nine years under Yahoo cofounder and fellow Forbes 400 member David Filo, before leaving in 2007. In 2009 started WhatsApp,now the world’s biggest mobile messaging service,with 600 million users. Facebook bought it for $19 billion in cash and stock in February.

9 ) Travis Kalanick
Age: 38

Net worth: $3 billion

Travis Kalanick, new to The Forbes 400, is the CEO of Uber Technologies, the hot ride-sharing service that raised $1.2 billion from private equity investors at a valuation of $18.2 billion in June. Uber is competing with taxi services across the U.S. and in 44 other countries around the world. FORBES estimates that Kalanick, a UCLA dropout, owns at least 17%. Uber is his third startup. His first venture an online file-exchange service was sued by the Motion Picture Association of America and the Recording Industry Association of America before filing for bankruptcy in 2000. His second company, another file-sharing company called RedSwoosh, was sold to Akamai in an all-stock deal valued at $18.7 million in 2007.

10 ) Nick Woodman
Age: 39

Net worth: $3.9 billion

GoPro, the popular wearable-video-camera company that Nick Woodman founded and heads, went public in June, and the stock has soared, tripling his net worth in a year and making him the biggest percentage gainer of The Forbes 400 this year. Woodman built the first camera prototype with his mom’s sewing machine and a drill and started the company in 2002. Woodman released his first video camera, a 35-millimeter waterproof film version, in 2004 and went on to sell it everywhere from surf shops to home shopping network QVC. Users strap their GoPros on bike helmets, surfboards and scuba gear. Revenues are forecast to hit $1.2 billion this year. Woodman grew up in Menlo Park, Calif. as the surfing son of an investment banker.

11 ) Chase Coleman
Age: 39

Net worth: $1.9 billion

Chase Coleman’s Tiger Global Management, which oversees some $14 billion, is one of the world’s most dynamic alternative money management businesses. His top-performing Tiger Global hedge fund, which is managed by Feroz Dewan, returned 15% net of fees in the first half of 2014. Tiger Global also beat the stock market and most rivals in 2011 and 2012, before cooling off somewhat in 2013. Coleman’s venture capital arm continues to raise significant capital to invest in fast-growing private tech companies like Facebook while they are still privately held. A “Tiger Cub” who trained under hedge fund legend Julian Robertson, Coleman serves as co-chair of the Tiger Foundation, which Robertson started to battle poverty in New York City !!!