Toners can last anywhere from a few washes to indefinitely, depending on the product used and how it is used. If you have very light hair, you may only need to tone it once or twice a week to keep your desired shade. However, if you have darker hair, you may need to tone it every time you shampoo. Because toners are typically applied to wet hair, they don't tend to last as long as other hair color treatments. This means that you may need to touch up your hair more often if you want to keep your color looking fresh.