On average, a perm is designed to last six months or less. The exact amount of time varies depending on the person.
As the hair grows, it comes in at its natural level of straightness, which pushes the permed hair further down and adds straight hair above it. Most people experience a hair growth of around 1/4 of an inch per month. Some people experience a slower or faster growth rate. Over time, a perm will naturally relax and begin to lose its shape. For short or shoulder-length hair, a perm can last an average of six months. If administered incorrectly, or if the person has fine hair that does not hold shape well, a perm can last as little as a few weeks.