You might think that the happiest point in a person’s marriage is those first few years of wedded bliss but new research, published in the journal Social Networks and the Life Course, gives credence to the idea that good things really do come to those who wait.

Married couples who are in it for the long haul see their happiness increase, admittedly only slightly, after the 20-year mark – or around the time of their China anniversary, if you’re into traditions.

“Marital happiness does not decline, on average, among spouses in stable marriages,” the study authors wrote. “Indeed, our results suggest that marital happiness increases slightly in the later years of marriage, especially for husbands.”

A team of researchers from The Pennsylvania State and Brigham Young Universities analyzed six waves of data from the Marital Instability Over the Life Course study, the first in 1980 and the last in 2000, to measure the ups and downs of 2,034 married individuals. In particular, they looked at the number of shared activities (think: eating dinner, shopping, and visiting friends), levels of marital discord and happiness, and marriage duration. 

In news that will shock no one, people whose marriages ended in divorce were more likely to report marital discord and fewer shared activities. Perhaps more surprising is that, despite popular opinion, marital happiness levels remained fairly consistent in spouses whose marriages survived the long haul – and, if anything, actually started to increase after 20 or so years together. This backs up other studies that have shown that married couples are at their happiest 40 years after tying the knot.

"[S]pending many years together provides opportunities for couples to experience even deeper levels of appreciation, closeness, and contentment," the researchers point out. (It may also help that the kids have grown up and moved out.)

There are a few limitations to the research, including the fact that a lot of the data was self-reported and, therefore, prone to bias. 

As the researchers themselves note, the data collection began in 1980 and ended in 2000 so the results may not apply to more recent marriages, especially as the study was limited to heterosexual wedded couples. Today, co-habiting partnerships are becoming more common, same-sex marriage is now legal in all 50 states, and polygamy is more accepted – generally, relationships are becoming more diverse. 

But although more research is needed, the takeaway message is something to feel positive about.

"Although divorce is common these days, about half of all marriages last a lifetime, and the long-term outlook for most of these marriages is upbeat, with happiness and interaction remaining high and discord declining," the authors conclude.

"This optimistic perspective is not sufficiently acknowledged or appreciated in the social science literature on marriage, which has tended to assume that relationship quality declines continuously for the majority of couples."