Both of these things are probably true: You have heard that 1 in 10 people are gay and you have no idea where that statistic came from.

Estimates of the size of the LGBT population have always been murky, bordering on mythological. The 1-in-10 figure first emerged out of post-World War II studies by the pioneering sexologist Alfred Kinsey, who reported that 10 percent of men were “more or less exclusively homosexual.” That number wasn’t perfect—and it’s been continuously revised—but it became a politically expedient tool in the Stonewall era.

Now, over 60 years after Kinsey’s death, new Gallup data shows that the estimated size of the U.S. LGBT population as a whole is getting closer than ever to the legendary “1-in-10” number—among millennials, at least.

Using Gallup data taken from interviews with over 1.6 million adults, demographer Gary J. Gates reported that 10 million Americans—4 percent of the population—now identify as LGBT.

That includes a record-high 7.3 percent of people born between 1980 and 1998 who now identify as LGBT—up from 5.8 percent in 2012. (This new data reinforces a 2015 conclusion from the Public Religion Research Institute—first highlighted by The Daily Beast—that “7 percent of millennials identify either as lesbian, gay, bisexual, or transgender,” based on a survey of 2,000 adults.)

But will that number ever reach 10 percent in the population at large?

“It’s not a completely unrealistic figure,” Gates told The Daily Beast. “Certainly it appears as if—given a little more time—it might, in fact, be [the case] that close to 10 percent identify as LGBT.”

Gates is one of the top demographers of the LGBT population in the United States, and the author of a widely-cited 2011 Williams Institute meta-analysis on the subject, which estimated that 3.5 percent of adults identify as lesbian, gay, or bisexual, and 0.3 percent identify as transgender. He told The Daily Beast that the increasing size of the LGBT population estimate can largely be attributed to “people feeling more comfortable and more willing to identify [as LGBT].”

But some groups are more willing than others to disclose their identity to a Gallup interviewer. Millennials, as Gates noted in his report, are responsible for “virtually all of the increases observed in overall LGBT self-identification,” which is unsurprising because they are “the first generation in the U.S. to grow up in an environment where social acceptance of the LGBT community markedly increased.”

In other words, it’s not the case that LGBT identity is suddenly rising in prevalence but that today’s young people are simply more forthcoming when asked about sexuality and gender on surveys. If you’re a baby boomer, think of it as a variation on that quote from the 1989 Kevin Costner classic Field of Dreams: “If you build LGBT inclusion, they will come out.”

And one sub-group of the LGBT community seems to be coming out—to Gallup, at least—in particularly large numbers.

“It’s very clear that some of the biggest increases are among women identifying as bisexual,” Gates informed The Daily Beast. “That’s what’s really driving a lot of these findings.”

Bisexual people, as Gates has previously reported, constitute a “slight majority” of the lesbian, gay, and bisexual community (PDF).

However, bisexual people are much less likely to be out of the closet than their lesbian or gay peers, with only 28 percent telling Pew in 2013 that “most or all of the important people in their lives” knew about their sexual orientation.

Increased bisexual self-identification among women, then, is an encouraging sign for a particularly maligned subset of the LGBT community.

Bisexual men, unfortunately, are subject to unique stereotypes and stigmas that may make it even more difficult to measure their number. (Only 12 percent of bisexual men told Pew that they were out to the important people in their lives.)

This uneven growth in LGBT self-identification across different sexual orientations and genders makes it challenging for Gates to confidently predict how quickly—or if—the estimated size of the LGBT population will rise beyond the 7 percent rate currently found among millennials.

“Ten years down the road, are men going to catch up or is that gap going to get bigger?” he wondered aloud.

But one thing’s for certain: The more LGBT people experience social acceptance, the more accurate our estimates of the size of the LGBT population will become.

In today’s social climate, research suggests that LGBT people may still be unwilling to self-identify as such on anonymous surveys. In one 2013 study from researchers at Ohio State University and Boston University—reported by Pew—the percentage of respondents who identified as non-heterosexual on a survey nearly doubled when they asked about sexual orientation in an indirect and even more anonymous way.

Gates points to discouraging indicators of contemporary anti-LGBT prejudice—like the fact that close to 30 percent of Americans think that same-sex sexual behavior should be illegal—as a sign that “we’re still quite a bit aways” from being confident that all survey respondents are comfortable disclosing their sexual and gender identity.

Demographers can make estimates and the government can try to ask about LGBT identity on the census, but until being LGBT is a total nonissue, we’ll never know the size of the population for sure.

Gates stresses that it’s still no cake walk for young people to come out—a response to the myths that it’s now “trendy” to be LGBT and that children are being “peer pressured” into being gay.

“Look, I can still offer you so many examples of why it is so difficult to be out as an LGBT person today,” he told The Daily Beast. “So the idea that it’s somehow just easy for any generation—particularly younger generations to come out—seems to me just ridiculous on the face of it.”

But generational change will almost certainly make coming out easier for everyone, young and old alike. And that’s why, if pressed, Gates does expect the estimated size of the LGBT population to climb ever closer to the mythical “one-in-10” mark.

“Based on research, I think the answer is probably that, in fact, these numbers are just gonna get closer and closer—and maybe exceed—10 percent down the road,” he said.