Robert Downey Jr. and his wife Susan keep their marriage strong with a '2-week' rule

The couple, who have been together for 21 years, don't let their hectic schedules get in the way of spending time together.

• Robert Downey Jr. and his wife, Susan Downey, follow a "two-week" rule to keep their relationship strong.
• The rule is that they don't go more than two weeks without seeing each other and their family.
• "Fortunately, we prefer to be a traveling circus when we can be," Downey told People.

Robert Downey Jr. and his wife, Susan Downey, don't let their busy schedules stand in the way of spending time together.

The couple, who have been together for 21 years, keep their relationship strong with a "two-week" rule that allows them to be with their family.

"We do have a two-week rule, which often feels too long, but we don't go more than two weeks without seeing each other and the family being together," Downey told People in a recent interview. "Fortunately, we prefer to be a traveling circus when we can be."

The couple have two children together: Exton Elias Downey, 12, and Avri Roel Downey, 9. Downey Jr. is also a father to a son, Indio Falconer Downey, 30, from a previous marriage.

But even with the rule, things don't always go according to plan, Downey said.

"You keep the basic rule of two weeks, and then you don't try and think too far ahead, because so much of what we do is oddly unpredictable," she said. Downey is a film producer and the cofounder of Team Downey, a production house that she started with her husband.

On the bright side, Downey's work schedule isn't as hectic as her husband's.

"The good news is I'm not in front of the camera, and so as a producer I end up with a little bit more flexibility in terms of location, of where I would need to be," she said.

Things would have been very different if they both had an acting career, Downey added: "I really admire and have a lot of empathy for couples who both have to be in front of the camera, because you get stuck and you have to make those choices."

The couple isn't the only one who has rules around maintaining a work-life balance: Blake Lively and Ryan Reynolds, who have been together since 2011, agreed not to work at the same time when they started dating so they could always put their personal lives first.

In a world that can feel increasingly isolated, making a point to spend time together meaningfully isn't just good for relationships, but for friendships too. Science has proven that having strong connections can lead to increased happiness, better health, and even a longer lifespan.