Good looks, humor, and charm can only get you so far when finding a partner.

You better be debt-free, too. With the average student loan debt per graduating student in 2018 nearing $30,000, it's enough to make some millennials pause before entering a serious relationship.

More than a quarter (27%) of millennials would definitely consider a prospective partner's student loan debt before entering a long-term romantic relationship with them, according to the "Master Your Money: Learn and Plan survey, conducted by Business Insider Intelligence.

Another 34% of respondents said they might consider a prospective partner's debt load, while nearly 39% said they wouldn't. The online survey polled 2,007 American millennials born between 1982 and 2000, fielded to a third-party sample between November 22 and November 27, 2019.

Men were significantly more likely than women to be put off by student debt in a romantic relationship. More men (32%) than women (22%) said they would consider it as a factor when choosing a partner, while more women (43%) than men (33%) said they wouldn't consider it.

The cluster labeled "yes" indicates how many respondents would consider student debt when dating someone. The cluster labeled "no" indicates how many respondents wouldn't consider student debt when dating someone. Ruobing Su/Business Insider

Respondents were also asked how much student debt would be a deal-breaker in a partner. While the average answer was $61,932, this varied significantly depending on whether the respondent would consider a prospective partner's debt load before entering a relationship with them: For those who would consider student loans as a factor, $47,575 was the average deal-breaker amount for student debt. That's a $20,000-plus difference from the average deal-breaker amount for those wouldn't consider it — $69,021.

That difference in debt thresholds makes sense: Those who would consider someone's student loans before dating them are less likely to tolerate a high amount of student debt in the first place. Those who wouldn't consider someone's student loans before dating them don't care as much about a partner's student debt and would, therefore, accept a higher amount of it.

Student debt can cause relationship rifts

Financial problems are one of the main reasons couples seek marriage counseling, and they're a leading cause of divorce. Student debt can just add fuel to the fire.

More than 10% of divorcees blame their divorce on student loan debt, according to a report by Student Loan Hero. But Taetrece Harrison, a family law attorney at Harrison Law Group, told Student Loan Hero that although student loans can intensify problems, she doesn't see them as a primary reason for divorce.

"Usually there's some relationship stuff that's going on, and then on top of that, they start to complain about the debt," she said. "I don't think [student loan debt] would be the driving factor, but it's definitely a secondary factor."

It can also translate into other kinds of financial struggles within a relationship. The same Student Loan Hero study found that nearly one-fourth of respondents kept their student loans a secret from their partner. Undisclosed debt is an example of financial infidelity, one of the biggest money-related reasons people get divorced.

Student debt is one reason why more millennials are increasingly signing prenuptial agreements before tying the knot, Leanna Johannes, senior wealth strategist at PNC Wealth Management, previously told Business Insider. Without a prenup, you may be left responsible for half of your spouse's outstanding debt after a divorce.