Married couples also tend to plan more, and accumulate for the long term. The commitment of marriage usually means people are also committed to goals from the start, whether it's conscious or not. The Zagorsky study said the commitment of married couples added up to 4 percent more wealth each year from a variety of sources such as homeownership and investing their savings. Once married, young people tend to start saving right away. (It's worth noting that singles may be catching up: Recent surveys have shown a surge in singles contributing to workplace savings plans at much higher rates, and that is likely to narrow the marriage wealth gap over time. Changes in workplace savings plan, such as the "opt-out" requirement that enrolls people automatically unless they decide otherwise, have led to a sharp rise in savings over the past two years.)
Experts also note that gender differences can make married couples less likely to veer too far in either direction on the risk-taking spectrum. Men and women tend to look at money matters differently, and that makes them natural diversifiers, which is a critical component of wealth accumulation.
It's true that men tend to be more confident with investing – often too much so – and they take more risks. Women tend to be more conservative. A study of affluent women released this week by Wells Fargo found that women overwhelmingly define themselves as more thrifty than their spouses.
"We found that women are more likely to define success in terms of peace of mind, and men define it as achievement in their careers," says Karen Wimbich, head of retirement for Wells Fargo. Those traits have a natural balancing effect, but a solid financial plan can help anyone, single or married, learn how to diversify their holdings.
But more than gender roles, creating a stable household creates some of the largest advantages. "If you look at the history behind a lot of legislation and tax benefits, they have always been drafted to encourage marriage, and people making commitments to marriage. It's been historically that case that forming a nuclear family has been financially encouraged," says Alex Popovich, a wealth advisor at JP Morgan Private Bank and an expert on financial issues in same-sex marriages.
The bottom line: Money goes to two places. It gravitates to where it can make more money or to where there is a safe harbor. A stable married couple can provide both, but so can a single person who plans for the future.