Clinically known as levonorgestrel tablets, the next menstrual period after a withdrawal bleed is calculated 28 to 30 days backward from the withdrawal bleed. Levonorgestrel is an emergency female contraceptive pill with the key ingredient being a high-dose progestin. It is a short-acting, high-dose progestin that inhibits ovulation and the implantation of a fertilized egg. Withdrawal bleeding mostly refers to drug-induced withdrawal bleeding after taking some emergency contraceptives. Most people will have withdrawal bleeding 3-7 days after using the pill, instead of the next menstrual period, so women who usually have a regular menstrual cycle will have their next menstrual period about a month after this bleeding. However, if the menstrual cycle is not regular, the time of the next menstrual period is not regular either.