It’s not your fault. It’s the ratio.

To all the young, college-educated women out there who feel like Donald Trump will probably become president before they find a decent, eligible man, take comfort.

According to author Jon Birger, you’re not imagining things. In “Date-onomics: How Dating Became a Lopsided Numbers Game,” out today, Birger, a former writer for Fortune and Money magazines, crunched demographic, census and other data to show that it really is historically rough out there for the ladies.

After noticing that his single gal pals were always complaining that “guys were ignoring them or were toying with them,” Birger decided to investigate. Based on his research, here are eight reasons why women can’t find a man — and strategies for increasing their odds.

You’re looking in Manhattan

The island is great for, say, watching a cheesy musical or spending $300 on a bottle of vodka. But for dating? Not so much.

“Because women have been graduating from college in 30-plus percent greater numbers than men for years, there are now four women for every three men nationally in the marriage-age, college-educated dating market,” Birger says.

In Manhattan, the numbers are even more dire, with 38 percent more young female college grads than male. Birger says the imbalance is also exacerbated by New York’s large population of gay males. Some 9 to 12 percent of men in Manhattan are gay, according to Gary Gates, a demographics expert at UCLA’s Williams Institute.

Other cities especially brutal for single women are Houston; Providence, RI; and Raleigh, NC. Better options include Silicon Valley, San Francisco, San Diego and Columbus, Ohio. The Bay Area, for example, attracts programmers, computer scientists and engineers — fields that are disproportionately male.

You went to the wrong college

The average gender ratio among US undergrads is now 57 percent women to 43 percent men. And some universities are even less of a sausage fest. At NYU it’s 61 to 39. At Boston University, 62 to 38.

“Facebook did a study a few years ago on how couples met, and it turned out that 25 percent met their significant others in college or grad school,” Birger says. “What was interesting is that the men who met their wives in college were not the ones who attended colleges that were disproportionately female. They attended colleges that were majority male.”

Want to increase your chances of getting hitched? Head to Rensselaer Polytechnic Institute (72 percent male) or Georgia Tech (66 percent), two institutions with way more guys than girls.

The men are playing you

“There’s a lot of social science showing that men behave differently in different relationship markets,” Birger says.

When faced with an oversupply of women, guys are more likely to delay marriage and play the field. Or, in other words, to act like guys.

Just finished DATE-ONOMICS by @jonbirger1 and it is life-affirming as a single woman in NYC. Also I’m moving. — Rachel Manwill (@rachelmanwill) July 11, 2015

And as reported by numerous publications, dating is out with young people and hookup culture is in. No need to wine and dine a potential mate when you can just swipe right. With the gender imbalance on college campuses, men are having a field day, and they may see no need to end their winning streak by settling down.

For women, however, the longer a girl settles for casual sex as opposed to a long-term relationship, the more chance she has of ending up alone.

You’re not issuing an ultimatum

“Ultimatums work in business and politics,” Birger says. “This notion that the only area of life you shouldn’t issue an ultimatum in is romance doesn’t make sense.”

Researcher John Molloy interviewed 3,000 couples right after they got their marriage licenses and found that 60 percent of the women were prepared to walk away if their guy suddenly declared he wasn’t ready.

If you are a single, 20-something college grad career woman, do not read Dateonomics. Spoiler alert: the stats are bleak. @marybeth0104 — Lauren France (@franzia86) June 26, 2015

You’re not making the first move

The aggressive women are the ones more likely to get the guy.

“I was talking about this with my rabbi, and he does premarital counseling,” Birger says. “Of the nine couples he had in counseling, seven of them shared a similar story: The guys all had several options, but they married the women who pursued them the most.”

And ladies, don’t worry about turning off guys by being too pushy.

“It’s a myth that men enjoy the chase,” Birger says.

You’re working in the wrong job

Slaving away in p.r., education, nursing, event planning or other female-dominant fields? Time to get a new job.

“Stanford sociologist Michael Rosenfeld reports that 10 percent of Americans meet their future spouses at work,” Birger says.

Some careers to consider: mechanical engineering (93 percent male), computer network administration (83 percent) and financial advising (74 percent).

You’re too religious

Consider dating a nonbeliever, even if it makes your grandma cry into her meat sauce.

“People who leave organized religion are disproportionately male,” Birger says. “Atheists and agnostics are also disproportionately male. An atheist meet-up would be a really good place to meet men.”

You’re too picky

“For the women who wait [to settle down], the dating pool gets much, much worse,” Birger says.

He likens it to a game of musical chairs. In the first round, fresh into the dating market, nearly every woman gets a chair. By the final round, the chances of losing soar to 50 percent.

For example, some 20 years ago a recent college-grad female confronted a dating market that had 117 recent college-grad men for every 100 women. Today that same woman, now 40, if still unmarried, faces a market in which nearly two-thirds of those formerly single men are hitched, and there are just 33 eligible men for every 50 women — 52 percent more women than men.

“None of this would matter if we were open-minded about who we dated,” Birger says. “The problem is, Americans — both men and women — have become more rigid about dating across socioeconomic boundaries.”

To find a mate, college-educated women should consider dating working-class men.

“In the future, we’re going to see more of what I call ‘mixed collar’ marriages,” Birger says.