A comparison of the economic impacts of marriage and being single may not be the most romantic thing to read on Valentine’s Day, but Bryan Caplan looks anyway:

I’m baffled by people who blame declining marriage rates on poverty.  Why?  Because being single is more expensive than being married.  Picture two singles living separately.  If they marry, they sharply cut their total housing costs.  They cut the total cost of furniture, appliances, fuel, and health insurance.  Even groceries get cheaper: think CostCo. …

But wait, there’s more.  Marriage doesn’t just cut expenses.  It raises couples’ income.  In the NLSY, married men earn about 40% more than comparable single men; married women earn about 10% less than comparable single women.  From a couples’ point of view, that’s a big net bonus.  And much of this bonus seems to be causal. …

Yes, you can capture some these benefits simply by cohabitating.  But hardly all.  And cohabitation is far less stable than marriage.  Long-term joint investments – like buying a house – are a lot more likely to blow up in your face.  And while there may be some male cohabitation premium, it’s smaller than the marriage premium.

If being single is so expensive, why are the poor far less likely to get married and stay married?  I’m sure you could come up with a stilted neoclassical explanation.  But this is yet another case where behavioral economics and personality psychology have a better story.  Namely: Some people are extremely impulsive and short-sighted.  If you’re one of them, you tend to mess up your life in every way.  You don’t invest in your career, and you don’t invest in your relationships.  You take advantage of your boss and co-workers, and you take advantage of your romantic partners.  You refuse to swallow your pride – to admit that the best job and the best spouse you can get, though far from ideal, are much better than nothing.  Your behavior feels good at the time.  But in the long-run people see you for what you are, and you end up poor and alone.