Millennials in couples are far more open about discussing their finances with their partners than older generations. And experts say that's helping make them happier.

While there are a lot of factors involved in making a relationship work, experts say money plays a key role. Nearly nine in 10 millennial couples (classified here as those aged 18 to 34) report being extremely or very happy in their relationships, according to a new survey from TD Bank of over 1,700 U.S. adults.

A full three-fourths of millennials in committed relationships say they talk about money on a weekly basis. That's about 9 percentage points higher than the share of Gen X couples, and an astounding 31 percentage points higher than the share of baby boomer couples, who say they have weekly discussions about their finances.

"We're in a better place than we used to be because younger couples are more willing and open to talk about their money — and to address it directly, right out of the gate," Dr. Jane Greer, a psychotherapist and relationship expert, tells CNBC Make It.

Roughly 80 percent of couples of all ages who talk about money at least once a week report being happy in their relationships, TD Bank found.