I’m entirely guilty of ignoring the fluctuating size of my breasts. For years, their size has changed as I’ve taken different forms of birth control. The only constant? My desire to live in sports bras and sports bras only. But recently, I realized my clothes were not fitting as well as they could and I wondered if, perhaps, a better bra wardrobe could fix things. Unsurprisingly, at least to everyone but me, it made a massive difference.

Once I was wearing the right size, I no longer reached for my sports bras on a daily basis. If you’re looking to figure out your own perfect fit, Ra’el Cohen, the head designer of ThirdLove, a bra company that helps women find their size through an app, divulged all her secrets.

A woman’s breast size naturally changes throughout her adult life — whether it’s from pregnancy, exercise, weight gain/loss, or other factors like birth control. So, your current size might not be the right size. “You may have been measured by an inexperienced person or you haven’t been measured often enough,” explains Cohen.

Before you buy a new bra, Cohen suggests checking in on the way your current bra fits, and gave us the rundown on four common red flags that may indicate you may be wearing the wrong size.

The band is higher in the back than the front. “If your band is creeping up in the back you’re most likely wearing a band size too big. It’s time to trade in your loose band and buy a smaller size so you have a snug fit,” she says. “You’ll know you’re in the right band size when you can slip two fingers underneath the back of the band. The band should be snug on the loosest hook, so when your bra stretches out you can continue to tighten it.”

Your straps are too tight or too loose. If you’re one of those women who strips off her bra the second you walk in the door, then you might have a strap problem. “Seems obvious, but as we wear a bra, the straps start to stretch out. We recommend tightening your straps every other month,” she says. “If that doesn’t work, it might be time to explore a different bra style. Usually full coverage bras have the narrowest set straps, which help to keep straps in place. Balconette and plunge bras tend to have wider set straps, so if you have narrow or sloping shoulders, the strap issue can be exaggerated with these styles.”

Your breasts are swimming in your cups. It might seem like an obvious fix is to go down a size if you have extra room in the cups, but that’s not necessarily going to fix things. Tightening the straps could be all you need, she says. But if that doesn’t work, try going down a cup size (or half a size, which is an option with ThirdLove).

The center of the bra (called a gore) is not laying flat on your chest. When the gore of a bra doesn’t sit flush against your skin, you might need a new kind of bra. “Sometimes the shape of the gore, is too tall for your breast shape,” Cohen says. “The more coverage a cup has, the taller the gore will be. If you’re finding that the gore won’t lay flat on your body, try a different cup shape like demi or plunge.”

To make sure you give your bras a long happy life, hand washing is always best, but in a pinch, Cohen says to machine wash bras on gentle in a mesh bag. Never put bras in the dryer, though, as heat breaks down the delicate fabrics and you won’t get as much life out of the bra.

And, if you simply need a new bra, either seek help from a professional or try ThirdLove’s FitFinder. Cohen recommends investing in at least six bras: two nude tshirt bras, one black tshirt bra, one lace bra, one nude strapless, and one black strapless.

“The fashion girl in me says 8,” she says, though. “So that you can have 2 that are just for fun.”

Ashley Ross is a freelance writer in New York City who has written for The New York Times, TIME, Cosmopolitan, Marie Claire, SHAPE, Glamour.com and more. She's a former gymnast and a graduate of the University of Florida.