If you’re a middle child...
Contrary to their reputation as insecure messes (example: Jan Brady), middle kids actually make stable and loyal partners. “One thing you’re not is spoiled,” Dr. Leman says. You probably grew up feeling like you got less attention than your siblings, and that drives you to work for every perk — including a happy relationship. Also in the “positives” category: You’re “a compromiser and negotiator,” Dr. Leman notes, so you’ll give your partner plenty of say in everything from how quickly your relationship progresses to where you go on vacation together. And your romance should be free of daily petty squabbles (middles hate conflict); instead, you try to put others at ease.
Your love challenge: Opening up. Have you ever been told you’re hard to read? “Middle children can be very secretive,” says Dr. Leman. “They got hammered by the first-born and swindled by the baby, so they keep their cards close to their chests.” You’re also not the best communicator when you’re upset. But if you learn to speak up instead of holding your anger in, you’ll have a more harmonious relationship.
Best match: Youngest child. “Middles aren’t as threatened by last-borns as they are by exacting first-borns,” says Dr. Leman, so the odds are good for open communication.

If you’re a youngest child...
You’re all about fun. The most outgoing of all in the birth order spectrum, youngest children live to have a good time (it may be because your parents were more laid-back by the time you came along). On a typical first date you’ll have your date laughing so hard that water shoots out his or her nose. In fact, “most famous comedians are youngest children,” says Dr. Leman. A partial list of famous examples: Jon Stewart, Jim Carrey, Ellen DeGeneres, Steve Martin and Eddie Murphy. And forget ho-hum plans like dinner and a movie; you love to do the unexpected, often on the spur of the moment. You’re the type to take someone to a party only to whisper, “Let’s get out of here” two minutes later... and then convince your date to take a road trip to Atlantic City or Vegas for the weekend.
Your love challenge: “Babies are the least financially dependable,” warns Dr. Leman (it comes from being, well, taken care of all your life). That means your date may be stuck picking up the tab when your credit card is maxed out. Also, some youngest children — not you, of course! — use that last-born charm and charisma to be a bit, ahem, manipulative, says Dr. Leman. That breed of baby will leave a date and sneak off to hit golf balls with pals or something similar, leaving the other person wondering what happened.
Best match: Either the oldest child (they serve as a good counterbalance in a parent-child sort of way) or middle child (they value friendships, so they totally understand why you love being the life of the party).

If you’re an only child...
You’re a rock-solid citizen — and a sweetie. “Only children are super-reliable,” Dr. Leman says. “They’re like oldest children taken to the extreme.” Growing up with only adults made you into a little grown-up early on — meaning you’re serious and dependable. You’re the rare person who will stay up half the night helping a friend or partner prep for a licensing exam or a big work presentation. You’re the type to move your partner’s car so he or she doesn’t get a ticket. Punctual and true to your word, onlies like you never leave a loved one waiting for a call or email. And you’re articulate, too, so your date can expect great conversations that really make a person think.
Your love challenge: Admit it — you’re a bit of a perfectionist. Maybe you send back steaks that aren’t cooked just so or point out a teeny-tiny stain on your date’s sweater. Also, you’re so cautious and pragmatic that you can be very slow to act (i.e., someone else has to make the first move).
Best match: Youngest child, because you balance each other out. The baby of the family adds spontaneity and romance, while you make sure you two aren’t dining by candlelight because the electric bill never got paid.