Oldest, Middle, Younger and Only Children—Who You’re Most Compatible with, Based on Birth Order

There are lots of ways to think about romantic compatibility, from personality types to the stars. Recently, though, I’ve been interested in birth order theory, which can be applied to everything from your spending habits to your love life. Whether you’re the oldest child, the “only”, the rebellious baby or forgotten middle sibling, birth order impacts your personality. So when it comes to birth order and compatibility, knowing how those traits can complement—or clash with—your partner’s birth order is useful. Should two youngest siblings date? Can a middle child and only child live in harmony? Below, I tapped two psychologists to give you the scoop. 

• Ehab Youssef is a psychology AI researcher at Mentalyc, a service that provides therapists with AI-powered note-taking technology. Previously, Youssef worked as a psychotherapist specializing in depression, anxiety, trauma and addiction. He holds multiple certifications, including from the Beck Institute for CBT, the European Psychiatric Association Certificate in psychodynamics and the Kasr El Ainy Yehia El Rakhawy Award. Youssef earned a masters degree in psychology from the University of Groningen in the Netherlands.
• Celeste Labadie is a licensed marriage and family therapist based in Colorado offering couples’ counseling, retreats and classes through her private practice, Willing to Love. Labadie holds a masters degree in marriage and family therapy from Regis University. 

Ah, the firstborn. As PureWow contributor Suzanne Zuckerman previously reported, the oldest child is the responsible, achievement-driven sibling. (Chalk it up to parental pressure, if you will.) Thus, they’re take-charge, action-oriented types who like to control things—and I’m saying this as an oldest child myself. But it’s not all intuition—Labadie has also observed in her practice that firstborns “are more rigid, more rule-bound and more focused on achieving than the other birth order positions.” This can be explained by the fact that they’re often expected to be available as a surrogate parent for younger siblings, in addition to being held to their first-time parents’ sky-high expectations.

If it sounds like the oldest child needs to *chill,* that would be correct. In this case, Youssef says that opposites do attract. 

“I’ve often noticed that the oldest children, who are used to taking on responsibility and leadership roles, pair very well with the youngest children,” he explains. “The oldest brings stability and structure, while the youngest adds a sense of fun and spontaneity. It’s a classic case of opposites attracting, creating a balanced dynamic where both partners feel valued.”

If opposites attract, then the laws of science still apply: Oldest siblings shouldn’t date fellow older siblings, as Youssef notes that a power struggle could ensue. Think about it: You have two people who are used to taking charge. “[That] can lead to conflicts over decision-making and control. It requires a lot of compromise and communication to make this pairing work smoothly,” he says.

Middle children are many things, but a squeaky wheel they are not. (Trust me, when I was a kid, we accidentally drove home without my middle brother, and no one noticed!) As such, they are the balancing center of a chaotic family ship. Youssef explains that middle children are typically great mediators and peacemakers with the ability to navigate varying personalities. They’re most compatible with the youngest siblings, who add a playful edge, and fellow middles, who understand the other’s need for balance and compromise. 

Trouble will arise for a middle child and only child, with Youssef explaining: “Only children often need a lot of attention and affirmation, which can be challenging for a middle child who is used to not being the center of attention. This dynamic can sometimes lead to feelings of neglect or frustration.”

As previously noted, the oldest/youngest pairing works particularly well, with the older sibling bringing stability and order and the youngest bringing joy and adventure. Middle and only children will get along thanks to the former’s adaptability to the latter’s need for fun and attention. “This creates a nurturing and balanced partnership,” Youssef notes.

Meanwhile, a pair of youngest children spells trouble, and I’ve seen this in my couple friends who are the babies of their families. “Practical responsibilities can sometimes fall by the wayside,” Youssef says. “Both are used to being taken care of, which can lead to challenges in managing everyday tasks and decision-making.”

Last but not least, the onlies. Youssef explains that eldest and youngest siblings would make a good match for the only child.

“Only children often appreciate the attention and care they receive from an oldest child, [and] the oldest sibling’s leadership and stability can provide a comforting structure. The youngest brings out the playful side of the only child, and the only child’s need for attention is met. It’s a dynamic that fosters both fun and security.”

Again, like repels like. Similarly to two eldest children, two only children will also butt heads as both are accustomed to being the center of attention. If neither can compromise, the couple will be headed for a gridlock. 

While birth order compatibility can say a lot about how a relationship will pan out, Labadie cautions that it’s not the ultimatum. 

“This is all very subjective because the relationship to each parent, in any birth order position, seems to have more impact on compatible pairings than birth order,” she notes. “Overall, birth order is not the only aspect of quality or successful pairings in couples. Instead, couples [should] focus on knowing how birth order impacts themselves and their partners. This understanding can offer more insight and compassion into how each of them adjusted to their family home life, and what it means for them in the present day.”