John Clifton Bogle works in a sunny office lined with books, piles of newspapers and research, paintings of Napoleon's battles, and Frederic Remington cowboy sculptures. At 87, he has slowed down only a little.

"I used to work from 6 a.m. to 6 p.m., but I don't do that anymore," said Bogle, who was ready to greet a reporter at 9 a.m. sharp at Vanguard headquarters in Malvern.

The inventor of the index fund is retired from actively running the investment-management company he founded four decades ago, but he heads the Bogle Financial Markets Research Center on Vanguard's campus.

Still hard at work, too, is his philosophy that few active money managers can beat the stock market, and that low fees make the difference over the long term. This year, Vanguard is approaching $4 trillion in assets, with $1 billion a day in new inflows.

That puts it well ahead of Boston rival Fidelity and just behind BlackRock, prompting an envious Wall Street firm to dub indexing a form of socialism.

As of Sept. 30, Vanguard managed more than $3.8 trillion in global assets, offering more than 350 funds to more than 20 million investors worldwide.

Indexing, Bogle said, combines "two great, but totally simple, ideas, which together have paid off. One is structure, the mutual structure of Vanguard; the other is the overall index strategy. Everything depends on cost in an index fund. The only way you can deliver the cost is run a mutual company."

Average expenses for an actively managed mutual fund run to about 2 percent annually. Investors can avoid that by using low-cost index funds - an idea Bogle proselytizes as often as he can.

He spoke recently at WHYY's Philadelphia studios in conjunction with a new PBS documentary on the savings crisis in America, When I'm 65. Sponsored by the Investor Protection Institute and the Pennsylvania Department of Banking and Securities, When I'm 65 examines Americans' shortfall in savings, and new ways of living and working in retirement. It airs nationally at 7 p.m. Nov. 13.

Bogle suggests fixing Social Security: first, by raising the tax on both employers and employees; second, by raising the taxable wage base, to perhaps $150,000 or more; and third, obviously, by raising the retirement age, with some exceptions for those who do manual labor.

"It's amazingly easy. All that's needed is political will," he said.

"Social Security passed in the 1930s. People were dying much earlier, and yet that 65-year age has still stood. Today, the service economy in America is far bigger, and people like me sit on our hindquarters all day. Those three things you could do that would not affect a lot of people."

Bogle understands that if 40 percent of Americans have no savings, "you can't force people to save when they have to eat. They have to survive on Social Security."

"Capitalism is a superb way of running an economy. But it also unfortunately has a tendency to vary the benefits widely. That's why we have this two-class society: the 1 percent and the 99 percent. The disparity in income is deeply regrettable. I don't know what we do about it exactly."

The 2008 financial crisis is responsible for today's low interest rates, which "enriched the 1 percent, and the aftermath . . . has hurt 75 percent of Americans who save. We [at Vanguard] brought out a money-market fund back in 1980 that yielded 15 percent back then on an annualized basis. Today, that's around 0.2 percent."

"I wonder how Middle America and Main Street are getting by at all. It's abnormal to have [rates] at these levels."

While interest rates have been abnormally low, stock returns have been abnormally high. When asked whether that could continue, Bogle noted that "the average return for the S&P has been 9.5 percent. That's the average for 25 years."

"Today, I'm saying maybe 6 percent: 2 percent from dividends and 4 percent earnings growth, going forward. That's the reality. I could be wrong easily!

"I divide market returns into two components: dividends and earnings growth. If dividend yields average 2 percent today and earnings growth 4 percent, that's a 6 percent investment return. So that's it. That's what corporate America will give us."

A mutual fund company has a huge cost advantage, he said. "If the market produces 6 percent a year, you get 5.95 percent after fees from an index fund, and 4 percent, minus 2 percent fees, if you're an active manager. It doesn't mean managers are stupid, they're just average.

"We've been in a remarkable period, a bull market of 40 years. It doesn't go on forever."

Pensions forecast returns of 7 percent a year, but Bogle said they won't be that high in the future.

"Corporate pensions total about $3.5 trillion out of $24 trillion in retirement savings. Corporate plans have to assume something that doesn't have the company put in too much money, otherwise that lowers earnings.

"In my book The Clash of the Cultures [Wiley, 2012], I show that corporations mostly use a 7.5 percent return assumption. But today, stocks yield 2 percent and bonds yield 2 percent, as well.

"Where are they getting the rest? They put money in hedge funds and private equity, and assume both of those give 20 percent return. Is there anyone who thinks that's going to happen?"

States use the same kind of assumptions, he said, "funding pensions from a tax base that would have to increase contributions."

"Taxpayers likely vote against that. So states are facing lower returns and greater longevity. And the payments are protected often by constitutions."

Private-retirement assets (IRAs, 401(k)s, 403(b)s) represent just $8 trillion out of $24 trillion in retirement savings.

"People are totally unaware of the value of starting early," Bogle said. "When you start at 25, you start saving $5,000 a year, it makes a huge difference due to compounding. You can capture the market return with an index fund. It sounds commercial, but I don't think it is. I have no interest in this place getting any bigger. Isn't $3.8 trillion enough?"

In a wide-ranging conversation, Bogle answered questions about how he paid for college: "I had a scholarship to Princeton, and I worked 40 hours a week, selling tickets at football season and as a waiter for a year or so. I didn't have any debt when I got through college. I worked vacations, I worked all the time."

And about his personal savings and investments now, including with John C. Bogle Jr., who works in finance: "Yes, my older son founded Bogle Investment Management. He's assiduous. He has 100 longs and 100 shorts, so he runs a true 'hedged' fund.

"If he has one long auto stock, he has one short. He's been able to deliver returns averaging 6 percent annually. It's all algorithms. . . . I invested a small amount in his small-gap growth mutual fund when he got started, as a show of confidence. He's done very well."

What else is in Bogle's portfolio?

"I own two portfolios. My largest single asset is my retirement plan here, which is tax-deferred, of course. My personal portfolio is somewhat different, but they're dominated by index funds. I'm about 50-50 stocks and bonds. Stocks are all indexed."

The Wellington Fund was his first holding. "I still own it. It's my legacy investment, it's what I owe to [Wellington founder] Walter Morgan," who gave Bogle his first job.

"Wellington Fund is about 96 percent indexed. We don't call it that. But the reality is that's the amount of the fund's return explained by the market averages. It's 65 percent S&P 500 and the other 35 percent is the Barclays Corporate Bond index. I've held it the entire time."

He also owns Vanguard Total Stock Market Index Fund and Vanguard 500 Index Fund. On the bond side, he owns Vanguard Intermediate-Term Investment-Grade fund, which holds mostly corporate bonds, and Vanguard Limited-Term Tax-Exempt Fund, which holds mostly municipal bonds.

Professional regrets? He has a few, he said.

"The specialty funds we [at Vanguard] introduced around 1983. I was going to do it better than Fidelity. Everything I did for marketing reasons I regret. You should only do it because it's a sound investment idea.

"I started Vanguard Specialized Portfolios, which is gone now. Specialty portfolios were an abject failure - except for Vanguard Health Care Fund. Out of the chaos came one of the great funds in our history."

Bogle, author of about a dozen books, said there are plans to update his 2007 The Little Book of Common Sense Investing.

"A new version will be out in 2017 with some info on retirement investing and asset allocation, the 10-year anniversary of its publication. I'd like to do another new book, a historical look at where Vanguard came from, probably my last."

He regularly hears from shareholders, he said: "Yes, my favorite is a letter from a waiter who worked at the Hilton. He wrote to say thank you, that he immigrated to the U.S. and started saving in the Vanguard S&P 500 fund."

"I get at least one letter a day," Bogle said. "Most are handwritten. And I try to answer every one."