There is no specific guideline on how long it takes stage 1 endometriosis to progress to stage 4, because it varies significantly depending on the patient. Many women develop stage 1 only to have it disappear entirely, according to Main Line Fertility & Reproductive Medicine.
Endometriosis is characterized by the growth of tissue outside the uterus which is similar to endometrial tissue, explains Johns Hopkins Medicine. The actual endometrial tissue lines the inside of the uterus instead. The four stages of endometriosis are determined by the extent and severity of these growths. Stage 1 is the mildest, and the most likely to clear up by itself with no medical assistance. Stage 4 is severe and may include multiple pelvic structures and large growths. Healthline also defines these stages as subtle, typical, cystic ovarian and deep endometriosis instead of numerical stages.
However, the progression in stages does not always mean that the symptoms are more severe. Some women experiencing stage 1 endometriosis have more pain and other symptoms than some women with stage 4. Main Line Fertility & Reproductive Medicine reports that the stages are mostly useful as a gauge of potential fertility issues, as women with more severe endometriosis may find it more difficult to become pregnant.
Although endometriosis is generally considered a progressive disease, the Physicians' Desk Reference notes that, as of 2015, there are no significant long-term studies proving that it gets worse in most women who suffer from the disease.