NEW YORK — As Lauren Smith and Matt Hendrickson drive home together, all conversation about work must stop a few blocks from their house.

The couple came up with the idea after starting a business together.

“That’s our cutoff point, so when we go into the house, we can have a normal personal life,” Lauren said.

Marriage and other long-term relationships aren’t easy. And running a small business is no picnic. Putting the two things together can make life complicated for the happiest of life partners.

Still, millions of people run businesses with their significant other every day. It’s not known how many couples own and run a business together, but the number runs into the millions. The most recent Census count, in 2007, showed 1.4 million companies that were co-owned and equally operated by husbands and wives. That doesn’t include businesses owned by unmarried domestic partners or same-sex couples. The Census counted another 2.3 million companies owned by spouses but primarily operated by either the husband or the wife.

There’s no formula for making a success out of a business that is owned by a couple — or for also keeping their home life happy. Many couples make disagreements part of their decision-making process. Some set their egos aside and listen to one another. And some, like Smith and Hendrickson, find that they need to take a break to keep working well together.

SETTING LIMITS: Smith and Hendrickson started Ascendify, a San Francisco firm that helps companies add social media to their online job postings, in April 2012, less than a year after they were married. Hendrickson brought 20 years of high-tech experience. Smith had worked in advertising.

Building a business together has its perks. Long hours working on a startup leaves little time for much else, the couple said.

“It became an all-inclusive, all-encompassing mind-share. We ended up working on it nights and weekends,” Hendrickson said. Besides their self-imposed curfew on the drive home, the couple schedules activities to keep the company from taking over.

“We’ll have a date night here or there, or go on a hike,” Hendrickson said. “If either of us talked about work on date night, we’d get in trouble with each other.”

The business is doing well enough that they’ve been able to hire two employees and plan to take on a third. The couple believes that they’re succeeding because they have something in common: They’re both risk takers.

“We have literally put our life savings into the business,” Hendrickson said. “It was a really risky decision, but we both had an entrepreneurial mindset.”

COMPROMISING: Natasha and Chris Ashton have learned a big lesson from owning a business together: The only way to end an argument is to compromise.

“We never reach an impasse,” said Natasha Ashton, co-CEO with her husband of PetPlan, a company that provides health insurance for pets. “One of us backs down and we make a joint decision.”

The Ashtons decided to start a pet health insurance business after their cat, Bodey, ran up $5,000 in vet bills. They had looked for insurance for her, and discovered it was relatively unknown in the U.S. while being very popular in Britain, where the couple comes from.

“It became apparent to us what a tremendous opportunity it was,” she said.

They started the Philadelphia-based company after they got their MBAs in 2003. It wasn’t always smooth. There were heated debates, and the Ashtons found that they needed to work out their differences.

“You can’t get held up or let emotions override your ability to make a decision,” Natasha Ashton said.

At first, the Ashtons were both involved in virtually every aspect of PetPlan. As it grew — it now has 80 employees — they each took on distinct roles. Chris Ashton handles the financial and insurance end of the business, while his wife focuses on marketing and public relations.

That has allowed them to expand their business. The couple started an animal health magazine called fetch! in 2008, and believe there are more ways to profit from their love of animals.

“Our main debates now are about strategy and where to allocate our resources,” Chris Ashton said.

GETTING PERSPECTIVE: Pam and Mark Fisher started their Boston-area construction business in 1991 after losing their jobs. Pam Fisher had worked for a small bank shut down by the government. The construction company where her husband worked also closed. The country was in recession and the job market was tough, so they launched Construction Coordinators, a contracting business that primarily handles renovations for restaurants, stores and offices.

The couple had the added stress of raising two young children. Mark Fisher landed one client right away through his former employer. After that, it took lots of cold calls to grow the business. Along the way, they had to learn how to reconcile their different approaches to a challenge.

“I tend to focus on the technical aspects and Pam focuses on the people aspect of it,” Mark Fisher said. “She’s really quick to understand what might be the motivator behind what happened, and I’m quick to figure out, how do we fix it?”

The Fishers say having their own interests is important. She belongs to organizations including a women’s real estate organization and a women’s networking group. He belongs to professional and trade groups focusing on architecture and entrepreneurship. Time apart provides perspective, Mark Fisher said.

“Having outside activities helps us remember why we’re here. It helps make it easier for me to step back and see where Pam’s coming from.”

They also made a point to celebrate the business within their family. After completing projects they brought the kids to see what mom and dad had been up to and took pictures at the sites. The outings resulted in an album that shows their business achievements and their children’s growth.

Over the years, they found that working together helped with personal matters like taking care of their children and their aging parents. They also have figured out how to keep the business running when family issues inevitably crop up. Recently, Pam Fisher was unable to make a client meeting because she had to travel to help an older relative with a health issue. Her husband covered for her — and also dealt with the aftermath of the blizzard that dumped two feet of snow in the Boston area.

“We both always know what’s going on at home or at work,” Pam Fisher said.

A LEARNING PROCESS: Natalie and Carlos Giron are still learning how to work together as business owners. It’s a difficult process because it’s complicated by worries about money.

Carlos Giron lost his job with a public relations firm at the end of 2008. His wife was working as a teacher at a Catholic school. The couple decided the best way to support themselves was to invest Carlos Giron’s $5,000 severance pay into a learning center and tutoring business in the New York City borough of Queens.

Natalie Giron runs Mrs. Giron’s Tutoring and Learning Center, working with children and their families, and overseeing as many as five part-time workers. Her husband runs the center’s website and does the marketing while also building his own business as a marketing consultant.

Owning a business has put a lot of pressure on the couple.

“When I was a teacher, I was more relaxed. He was the main breadwinner,” Natalie Giron said.

Carlos is stressed, too. They have had arguments over the direction of the business, like whether to raise fees. At one point, Natalie Giron questioned whether they should stop running the business together — or if they should even run it at all.

“If the business brings us money but ruins our relationship, it’s not worth it,” she told her husband.

Slowly they have learned to work better together. It helped when Carlos Giron did some work with the children, and began to understand his wife’s point of view.

“It’s only recently that I have changed my mindset, and he has also changed his way of looking at things,” Natalie Giron said. “Both of us have learned how to trust each other, that we mean well and we want to share our partnership.”

A WORK IN PROGRESS: Amber Wallace and Jill Kingdon have been a couple for 10 years, married for 4½ years, and owned Dowitcher Designs for nearly seven years. Although it can be rewarding and fun to be a couple running a company that provides Web and print design services, there are times when they’re not sure they want to do this forever.

“When we’re very busy and something didn’t get done, one of us will get upset and it will turn into an argument — those are the sorts of things that usually heat up to a ‘maybe we shouldn’t be doing this’ scenario,” said Wallace, CEO of the Santa Barbara, Calif., firm.

But it’s not just the heat-of-the-moment discussions.

“We do talk about, what if we have kids? One of us would have to be less involved, and how would that be structured?” Wallace said. The couple married in 2008 during the four months that same-sex marriage was legal in California.

Wallace and Kingdon can still find it hard to stop their business from taking over their personal life. They try to keep weekends work-free by scheduling a Monday morning meeting to talk about what’s going on at Dowitcher Designs. But sometimes, in the midst of what’s supposed to be time off, they find themselves strategizing about how to solve a problem or handle a project.

They also have to remember sometimes to be spouses, and forget for the moment that they own a business together.

Sometimes, Wallace said, she finds herself telling Kingdon: “I’m putting on the wife hat and I just want to complain. I don’t want to talk about solutions — I just want to rant!”