To really understand what’s going on with the American economy, don’t look at the headlines. Don’t look at the unemployment rate or the trade balance or the deficit. Don’t even look at what’s happening today at all: Look at what happened 46 years ago.

And what happened then? Fewer Americas were being born, points out Harry S. Dent Jr. in “The Demographic Cliff: How to Survive and Prosper During the Great Deflation of 2014-2019” (Portfolio).

Following the Baby Boom, which peaked in 1961, came the Baby Bust, a long slow decline in the birthrate. Those babies grew up and began spending in accordance with highly predictable patterns.

People tend, for instance, to buy houses at about the same age — age 31 or so. Around age 53 is when people tend to buy their luxury cars — after the kids have finished college, before old age sets in. Demographics can even tell us when your household spending on potato chips is likely to peak — when the head of it is about 42.

Ultimately the size of the US economy is simply the total of what we’re all spending. Overall household spending hits a high when we’re about 46. So the peak of the Baby Boom (1961) plus 46 suggests that a high point in the US economy should be about 2007, with a long, slow decline to follow for years to come.

Anyone find that convincing?

Dent, a business consultant, stock-market prognosticator and author who says now is the time to sell stocks, has plucked an old argument off the dusty shelves of 1980s political rhetoric (“We’re nothing like Japan! And that’s horrible!”) and given it a new coat of paint: We’re exactly like Japan! And that’s horrible!

Japan’s stock market is still 65% below its 1989 peak. Their spending problem (currently being given a boost by a gigantic stimulus) is really, says Dent, an aging problem.

As the Japanese have hit their 60s and 70s, they became stingier. Artificial, forced spending like government stimulus is not going to spark real voluntary spending because that isn’t what old people do. They’ve already paid for their houses, cars and their children’s schooling. Merchants try to goose lackluster sales by cutting prices, which increases the incentive for people to save their money, expecting things will be cheaper in the future than they are today.

That’s a deflationary spiral, and Dent sees it coming here next, and soon.

Post-crash, the US economy has been limping along for nearly five years despite a series of massive fiscal and monetary stimuli. A principal reason for what growth we have had is the spending pattern of rich people, who tend to put off their big purchases years later in life than the average. Their peak spending year should be, according to Dent, 2014.

And, no, immigration isn’t going to save us; even adjusted for immigration, the overall US population is aging. (Moreover, an anemic economy attracts fewer foreigners: Net new immigration from Mexico dropped to zero between 2005 and 2010).

Lost in the discussion of this week’s Congressional Budget Office report (which said 2.5 million fewer Americans would be working because of Obamacare) was its prediction that aging will be a major drag on growth: “Beyond 2017,” said the report, “CBO expects that economic growth will diminish to a pace that is well below the average seen over the past several decades [due in large part to] slower growth in the labor force because of the aging of the population.”

Economically speaking, winter is nowhere near an end. Spring isn’t due until about 2019, which is when the economy will receive a boost from the spending power of the Echo Baby Boom of the 1980s (which peaked in 1990) and the concurrent wave of immigration. In 2019, these second Baby Boomers will buying their first houses.

Dent’s book is, for all its charts and graphs, startling in its simplicity. Single answers to complex systems aren’t generally very convincing. And statistical models that successfully predict the past may be enticing, but how useful are they? The past never perfectly anticipates the future.

And yet the demographic numbers are so large that they’re bound to play a central economic role.

Implicitly, Dent is saying: Don’t blame politicians, the decline of manufacturing, education or cheap foreign imports for the economic stagnation that has already begun and will continue for many years. Blame your parents and grandparents for losing interest in having children back in the Sixties.