You’re about six beers deep and finally—after several overpriced dinners and cocktails—you’ve convinced a super hot chick that you’re the all-around awesome guy she initially hoped you'd be. Score! So as you head back to your place and things get heated, there’s no shot you’re killing the mood with a condom...right?

Bad idea. Terrible idea. In fact, that logic is so flawed, we’re going to go ahead and counter it with the ultimate mood killer: In the first year of a baby’s life—between doctor visits, clothing, food, and everything else, a parent can expect to spend more than $10,000. (Yeah. Let that sink in.)

So unless you’re ready to trade beer for baby formula? Read this—our expansive guide to making sure you don’t knock her up. Because even if you play it safe most of the time, you’re probably screwing up in ways you didn’t even know were possible. And like your old man always said, it only takes one mistake.

1. The Mistake: You think having sex standing up prevents pregnancy.

The Potential Damage: We couldn’t believe that nearly 1 in 5 of men buy into this, but according to a 2010 study, it's true. Yikes. “The law of gravity is not a contraceptive,” says Debby Herbenick, Ph.D., the co-director of The Center for Sexual Health Promotion. That’s a seemingly obvious assessment, right? Use it.

2. The Mistake: You blindly grab some lube.

The Potential Damage: Always, always, always check what your lube is made out of—otherwise, that condom might do jack. “Oil-based or petroleum-based lubricants like mineral oil or massage lotion can destroy condoms, making them more likely to break,” says sexologist and sexuality educator Megan Andelloux.

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3. The Mistake: Your hands are sweaty, so one of you tears the condom package with your teeth.

The Potential Damage: Using items like knives or scissors—even your teeth—to open a wrapper will make it very easy to mistakenly poke a hole in the condom. (In one study, dudes who did so were about three times more likely to encounter breakage.) Think about it—do you really want sharp objects coming anywhere near the super-thin barrier that stands between you and fatherhood?

4. The Mistake: You put the condom on—but don’t leave any space in the tip.

The Potential Damage: If you covered up a faucet with your hand and turned it on full blast, where would the water go? See what we’re sayin’? It’s not rocket science. So leave approximately half an inch at the top of the condom to properly “catch” your sperm, says Herbenick; without this wiggle room, you’re risking breakage.

5. The Mistake: You don’t use a condom because she’s on the Pill. 

The Potential Damage: If you’re in a relationship, you should trust that she’s true to her word, but for a one-night stand? It’s not worth the risk. According to the Centers for Disease Control and Prevention, birth control pills are between 91-99 percent effective in preventing pregnancy—but the Pill plus a condom gives you close-to-perfect protection. Your call.

6. The Mistake: You were wasted and couldn’t find a condom...so you didn’t use one.

The Potential Damage: Sure, it’s an understandably awkward situation if you’re about to “get it in” and can’t figure out where the hell you put the condom. But is it more awkward than becoming a daddy if you’re not ready for a kid? Get off your ass and search a little harder, or walk to the store and pick up an extra pack. According to the World Health Organization, with perfect use, condoms prevent pregnancy 98 percent of the time. That’s pretty damn good.

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7. The Mistake: You’ve had the same condom hanging out in your wallet forever.

The Potential Damage: Using a condom that hasn’t been properly stored might get you into a situation worse than the sexual slump you just endured. According to Herbenick, extreme heat or cold can damage the latex used in condoms, so the best spot for stashing them is a cool, dark, dry place—like in your nightstand—or a small, hard case (think: one made for business cards). And if you’re really trying to be a douche about the whole thing, there's alwasy this $200 Swarovski crystal condom compact.

8. The Mistake: You’re not putting lube inside the condom.

The Potential Damage: Those marathon sex sessions you’ve been having (nice work, bro) are bound to wear down the condom, making it dry and prone to ripping. “Always use lube inside the condom. It prevents breakage and plus, it actually feels so much better for the condom wearer,” says Andelloux. Remember: check the type of lube before you apply, and just use a drop—too much can make the condom slip off.

9. The Mistake: You take the condom off before the sex is over. 

The Potential Damage: If you're patting yourself on the back for using a condom in the first place... don't. Taking a condom off too early on into sex "can directly compromise the efficacy of condom use," according to a recent study from The Journal of Sexual Health. But you know that, silly! So if you play by the rules and keep that sucker on the entire time, it's 98 percent certain (see no. 6) you won't have to worry about becoming a daddy. (Just be sure you hold the base of the condom during withdrawal to make sure it doesn't slip off or leak you-know-what.) 

10. The Mistake: You don’t need condoms—you’re a “pull-out pro.”

The Potential Damage: You might think you have impeccable timing, but even if you do pull out in time, it’s still possible to get her pregnant. How? According to Planned Parenthood, your pre-ejaculate can pick up enough sperm left in your pipes from your last ejaculation to fertilize an egg. Whoa. Now, urinating between ejaculations might help, but as they say, it’s always safer to wrap it before you tap it—and the risk-taking for your non-sexual adventures.

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