This is one of the most common bra problems and a good sign that your in the wrong fitting bra. If your band rides up your back it could be for a number of reasons. The most common reason for your band riding up is the band is too big. Most often women are in the wrong band size. Going down a band size will probably fix your problem. However, remember that when changing the band size you will also need to adjust the cup size accordingly. For example if you are a 36D and the band is to large, you would want to try a 34DD. Also adjusting your straps to tight will cause your band to ride up, it can also cause sagging in the front. Readjusting your straps should be an easy fix for this problem. Lastly another very common reason for your band riding up would be your bra is streched out. You bra won't last forever, and the older it gets the less support it will offer. Its suggested to replace your bra and get refitted every six months as our bodies are constantly changing. Dont be surprised if your bra size has changed since your last measuring.
In a proper fitited bra, the band is responsible for 80% to 90% of the support. It should fit comfortably around your torso, and parallel to the floor. The band should be snug but you should be able to slide two fingers between the band and your skin. If the band is too tight, digs into your side or is uncomfortable, it's too small. Signs that your band size is too big include breasts falling out from the bottom of your bra and your bra back riding up. A correctly sized band will fit firmly around you and not ride up in the back. A new bra should be able to pass this test with the clasp on the loosest fitting - this allows you to tighten the bra as it stretches with wear and washing. Avoid buying a bra where the best fit is the bra's tightest hook, You always want to buy a new bra that fits on its loosest fastening position.