“I have a Chanel bag fetish,” admits Stella (not her real name), a married corporate attorney who works in Midtown. “I have five pretty expensive bags. People ask me, ‘What does your husband say about that?’”

This does not sit well with Stella. “I’m like, ‘He’s not saying anything. This is my money. And he knows I work really hard for it!’ ”

Stella, 35, like an increasing number of New York women, is the primary earner in her household. Her husband, 36, works too, in sales — but her heftier paycheck ($340K to his $100K) is the reason they’re able to afford the big house upstate, the cars, the college funds for the kids (not to mention the thousand-dollar arm candy).

She’s always been ambitious and career-minded, so Stella’s not surprised that she’s earning big bucks — but, she admits (under guise of anonymity), this wasn’t the way she imagined her relationship dynamic would play out. “I had always known that I wanted to make money and be successful,” she says. “But it was still ingrained in me that the man makes more.”

This “Mad Men” paradigm is starting to look like a relic, though. A US Census study out last year found that 4 in 10 American households with children under age 18 have a woman as either the primary or sole breadwinner — a huge jump from earlier decades (and quadruple the amount in 1960).

We see this seismic shift playing out in the celebrity spotlight, where A-list actresses are proudly pairing up with men of more modest means. Natalie Portman’s husband, Benjamin Millepied, is a ballet choreographer; Scarlett Johansson is engaged to a French journalist; Anne Hathaway’s husband is a lower-wattage actor and jewelry designer. Julia Roberts’ husband is a cameraman, while Oprah’s significant other is . . . well, he’s Stedman. Media moguls Marissa Mayer and Sheryl Sandberg both out-earn their tech-sector husbands.

Patti LuPone isn’t just a theatrical breadwinner (her husband, Matt Johnston, is a cameraman) — she also played one on two episodes of “Girls” this year, in which her TV spouse complained that he was a frustrated writer who was constantly getting called “Mr. LuPone.”

Like any major cultural change, this one comes with growing pains: Sorting out new gender roles can be tough on both partners in a household where she’s the one who brings home the bacon, no matter how progressive both parties might think they are.

Boerum Hill-based author Farnoosh Torabi, a personal finance expert, speaker and coach, addresses this conflict in her new book, “When She Makes More: 10 Rules for Breadwinning Women.” Out Thursday, it arrives at a moment when statistics show women outperforming men in several key areas — but still dealing with outmoded gender role expectations.

“Women are making bigger strides in the academic and professional worlds; they’re buying more property than men, starting businesses faster than men,” says the 34-year-old Torabi. According to Labor Department statistics out in March, 32 percent of 27-year-old women had a bachelor’s degree, while only 24 percent of men did. And a National Association of Realtors study in 2012 found that 18 percent of single women were homeowners compared to just 10 percent of men.

“Yet,” says Torabi, “there’s this rude awakening, after you finish climbing the mountain — you might end up being the breadwinner in your relationship without any idea how to make it work.”

Specifically, she says, there are myriad small resentments that can build up between partners. “If there’s one person who feels their paycheck defines their self-worth, that can be a tough thing to get over,” she says. “On her end, it could be feeling resentful that she’s taking on so much. Or him feeling ‘less than,’ because of not being able to provide financially — which, for men, has always been what they were expected to do.”

She knows her source material intimately: Torabi has been a primary earner for years. Her husband, Tim, works in software at a startup. “As our careers evolved, mine has been on the up and up whereas his has been a little more up and down. So today we’re at a point where it’s a big income difference,” she says.

For many women (including the author), bearing the mantle of breadwinner comes with a significant amount of pride — but also pressure. “I’m responsible for the financial stability of my family. That’s more stressful than I thought,” says Jennyfer Bagnal, a 40-year-old private tutor in Crown Heights. Fortunately for Jennyfer and her husband, a 39-year-old documentary filmmaker and adjunct professor at NYU, they have a functional system worked out: He does the lion’s share of the child care and the housework, while she works long hours in her independent business.

But not everyone has such a clear-cut arrangement. Nancy (not her real name), a 49-year-old consultant who lives in Brooklyn Heights, earns about $75K to $100K more than her boyfriend, who’s “in the arts.” But she also ends up doing the majority of the housework, much to her annoyance. “I think it goes back to the female-male thing,” she says. “Stereotypes that we’re stuck with. I do all the laundry — it’s just the nature of it.” Nancy says her boyfriend offers some currency in terms of access to the New York creative scene — but hobnobbing is hardly the same thing as cash.

“I own my place, and he pays toward the rent. Some months he can’t pay — but it’s better when he can,” says Nancy, who’s eager to read Torabi’s book. “It’s going to save a lot of marriages!” she says. “I wish I had had it years ago. It might have helped with my own marriage.” Resentment over her earnings contributed to her divorce, she says.

It also lingers for Stella, who says arguments bubble up over her lack of investment in chores. “I had my husband make up [the economic difference] in sweat equity,” she admits. “He used to do all the cooking, all the cleaning. Now we have a service, but he pays for it. In my mind, that’s his responsibility.”

If her husband objects, “that’s when I’ll throw it in his face that I’m the reason we have this house. I know that’s something I shouldn’t do, but it’s my way of defense.”

Stella’s occasional outbursts reflect a recent study from Working Mother Media, which found breadwinners who ended up in that role by default felt less satisfied than women who consciously made the arrangement. The latter number seems to be relatively small: In a survey group of 2,000 working mothers, only 29 percent had chosen the role. It just sort of worked out that way, said 71 percent. This is especially true post-recession, in which the majority of job losses were men’s, and where women were quicker to bounce back.

In another finding that’s worrying defenders of marriage, the increasing prevalence of high-earning women may be adversely affecting their chances of tying the knot, according to researchers at the University of Chicago Booth School of Business. Stella sees this firsthand at her law practice. “There aren’t that many women at my level, unfortunately,” she says, “and the ones who are are mostly single. Men don’t want to date a successful woman — they want the 20-year-old bimbo. I’m like, ‘Well, I’d much rather have a mate that I love who makes less than me than no mate at all!’ ”

But the bimbo-seeking men are clinging to an old world order that’s shifting under their feet. In fact, says another new book, alpha women like Stella are doing exactly the right thing by finding a modern-minded mate; this is a new paradigm in which the evolutionary-biology notion of pairing up with the most dominant male may not be relevant. In “The Alpha Woman Meets Her Match: How Today’s Strong Women Can Find Love and Happiness Without Settling,” author Sonya Rhodes chronicles the virtues of men who are flexible, communicative and collaborative rather than chest-thumping alphas.

For Torabi, communication is absolutely key to the success of the female breadwinner, and she urges others to make it a priority. Power is not in who holds the paycheck, she says; it’s in the strength of how a couple works together to achieve their shared financial goals.

“My husband and I talk very candidly about the disparity,” says Torabi, who is pregnant with their first child. “He knows he may never make as much as [I do], but he is interested in pursuing a career with more income potential, if for no other reason than to get me to be less stressed. I would love for him to be the breadwinner one day. It’s a really awesome position to be in!”