Robert Downey Jr. and wife Susan swear by this one rule in their 18-year marriage

Robert Downey Jr.’s wife, Susan, is pulling back the curtain on how they keep their 18-year ironclad marriage strong.

“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,” Susan, 50, told People in an interview published Thursday.

“Fortunately, we prefer to be a traveling circus when we can be,” the producer added of their son Exton, 12, and daughter Avri, 9.

Robert Jr., 58, also shares his son Indio, 30, with his first wife, singer Deborah Falconer.

“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. You just never know.”

Susan continued, “Someone might get sick, or there might be a shutdown, or this or that. So you just have to have some basic things in place, and then you have to be willing to flow with the rest of it.”

The “Tropic Thunder” star quipped, “It just gives me, honestly, something to attach my neurosis to that’s positive.”

The Downeys had a busy award season as Robert Jr. won a British Academy Film Award, Critics’ Choice Movie Award, a Golden Globe, a SAG Award and an Oscar for his role as Lewis Strauss in “Oppenheimer.” He thanked Susan in all of his acceptance speeches.

“I’d like to thank my veterinarian — I mean my wife, Susan Downey, over there,” he joked at the Oscars. “She found me a snarling rescue pet and you love me back to life. That’s why I’m here.”

The “Ironman” star said of his bride at the SAG Awards, “For 22 years, she has flawlessly portrayed a sane and rational individual who is happily married to an actor.”

The pair met on the set of the 2003 film “Gothika,” on which Susan was working as a producer at the time. Robert Jr. proposed three months later and they wed in 2005.