If your bra rides up your back, it definitely does not fit properly. There are three reasons this may be happening and by fixing these problems, you will be more comfortable and supported in your bra.
Loosen Up the Straps!
The first reason your bra band may be riding up is that you may be adjusting your bra straps too tightly. If your straps are too tight, the band will ride up. It is a common misconception that tight bra straps will create lift; the support comes from the band, not the straps. Loosen your straps and see if this solves your problem.
Get the Perfect Fit
The second reason your bra band may be riding up is the most common - your band is too big. If your bra fits correctly, your bra band will sit snuggly and will create a straight line across your back. If your band is too loose, the back of the bra will rise which will cause the front to droop and sag. Not cute!
To fix this problem, try going down a band size. Please note that the amount of space in the cup is directly related to your band size. For instance, the cup on a 38D bra has larger cups than a 36D. This means that when you go down a band size, you will have to go up a cup size. So if you're wearing a 38B and need a tighter band, you should try a 36DD.
The third and final reason your bra may be rising up your back is that your bra is too old and stretched out. If the bra only recently started behaving this way, try putting it on a tighter setting. But if you're already on the last hook, your bra is "dead." In this case, bury your dead bra and buy a new one in your proper size. Read: shopping time!