Natural FP - Calendar method
This method requires you to track how many days each of your menstrual cycle takes, for a period of about eight months. This will give you a good picture of how long your cycle is. A menstrual cycle begins on day one of your period and ends on day one of your next period. Once you have this record, your health care provider can help you predict your fertile days. This method is not 100% accurate and it would be wise to combine it with other fertility methods to increase the efficacy.
Attribution: Avallain