For decades, we have been hearing that the baby-boom generation was like a pig moving through a python–bigger than the generations before and after.

That’s true. But that’s also a very misleading metaphor for understanding the demographic forces that are driving up federal spending: They aren’t temporary. The generation born between 1946 and 1964 is the beginning of a demographic transition that will persist for decades after the baby boomers die, the consequence of lengthening lifespans and declining fertility. Putting the federal budget on a sustainable course requires long-lasting fixes, not short-lived tweaks.  

First, a few demographic facts.

As the chart below illustrates, there was a surge in births in the U.S. at the end of World War II, a subsequent decline, and then an uptick as baby boomers began having children.

Although the population has been rising, the number of births in the U.S. the past few years has been below the peak baby-boom levels, possibly because many couples chose not to have children during bad economic times. More significant, fertility rates–roughly the number of babies born per woman during her lifetime–have fallen well below pre-baby-boom levels.

Meanwhile, Americans are living longer. In 1950, a man who made it to age 65 could expect to live until 78 and a woman until 81. Social Security’s actuaries project that a man who lived to age 65 in 2010 will reach 84 and a woman age 86.

Put all this together, and it’s clear that a growing fraction of the U.S. population will be 65 or older.   

The combination of longer life spans and lower fertility rates means the ratio of elderly (over 65) to working-age population (ages 20 to 64) is rising. As the chart below illustrates, the ratio will rise steadily as more baby boomers reach retirement age–and then it levels off.  

Simply put, this doesn’t look like a pig in a python.  

So what do these demographic facts portend for the federal budget?  In simple dollars and cents, the federal government spends more on the old than the young. More older Americans means more federal spending on Social Security and Medicare, the health insurance program for the elderly. On top of that, health care spending per person is likely to continue to grow faster than the overall economy.

The net result: 85 percent of the increase in federal spending that the Congressional Budget Office projects for the next 10 years, based on current policies, will go toward Social Security, Medicare and other major federal health programs, and interest on the national debt.

Restraining future deficits and the size of the federal debt mean restraining spending on these programs or raising taxes–and probably both. One-time savings or minor tweaks won’t suffice. Nor will limiting the belt-tightening to annually appropriated spending.

The fundamental fiscal problem is not coping with the retirement of the baby boomers and then going back to budgets that resemble those of the past. The fundamental fiscal problem is that retirement of the baby boomers marks a major demographic transition for the nation, one that will require long-lived changes to benefit programs and taxes.

Tomorrow, President Obama unveils his last budget, and we’re sure to see plenty of proposals for spending on education and skills. In the past, the Administration has focused on investments in early childhood education, community colleges, and infrastructure and research. From a budgetary standpoint, the problem with these investments is how to capture their benefits as well as their costs.

First step: find out what works. The Obama Administration has been emphatic about the need for solid evidence in deciding what to fund. The good news is that we now have quite a lot of it, showing that investing in human capital from early education through college can make a difference. Not all programs are successful, of course, and we are still learning what works and what doesn’t. But we know enough to conclude that investing in a variety of health, education, and mobility programs can positively affect education, employment, and earnings in adulthood.

For example:

1. Young, low-income children whose families move to better neighborhoods using housing vouchers see a 31 percent increase in earnings;

2. Quality early childhood and school reform programs can raise lifetime income per child by an average of about $200,000, for at an upfront cost of about $20,000;

3. Boosting college completion rates, for instance via the Accelerated Study in Associate Programs (ASAP) in the City University of New York, leads to higher earnings.

If such estimates are correct (and we recognize there are uncertainties), policymakers are probably underinvesting in such programs because they are looking at the short-term costs but not at longer-term benefits and budget savings.

First, the CBO’s standard practice is to use a 10-year budget window, which means long-range effects are often ignored. Second, although the CBO does try to take into account behavioral responses, such as increased take-up rates of a program, or improved productivity and earnings, it often lacks the research needed to make such estimates. Third, the usual assumption is that the rate of return on public investments in human capital is less than that for private investment. This is now questionable, especially given low interest rates.

A hot topic in budget politics right now is so-called “dynamic scoring.” This means incorporating macroeconomic effects, such as an increase in the labor force or productivity gains, into cost estimates. In 2015, the House adopted a rule requiring such scoring, when practicable, for major legislation. But appropriations bills are excluded, and quantitative analyses are restricted to the existing 10-year budget window.

The interest in dynamic scoring is currently strongest among politicians pushing major tax bills, on the grounds that tax cuts could boost growth. But the principles behind dynamic scoring apply equally to improvements in productivity that could result from proposals to subsidize college education, for example—as proposed by both Senator Sanders and Secretary Clinton. Of course, it is tough to estimate the value of these potential benefits. But it is worth asking whether current budget rules lead to myopia in our assessments of what such investments might accomplish, and thus to an over-statement of their “true” cost.