It doesn't seem like much to ask for—a 5 percent return. But the odds of making even that on traditional investments in the next 10 years are slim, according to a new report from investment advisory firm Research Affiliates.

The company looked at the default settings of 11 retirement calculators, robo-advisers, and surveys of institutional investors. Their average annualized long-term expected return? 6.2 percent. After 1.6 percent was shaved off to allow for a decade of inflation, the number dropped to 4.6 percent, which was rounded up. Voilà.

So on average we all expect a 5 percent; the report tells us we should start getting used to disappointment. To show how a mainstream stock and bond portfolio would do under Research Affiliates' 10-year model, the report looks at the typical balanced portfolio of 60 percent stocks and 40 percent bonds. An example would be the $29.6 billion Vanguard Balanced Index Fund (VBINX). For the decade ended Sept. 30, VBINX had an average annual performance of 6.6 percent, and that's before inflation. Over the next decade, according to the report, “the ubiquitous 60/40 U.S. portfolio has a 0% probability of achieving a 5% or greater annualized real return.”