NFP stands for "Natural Family Planning" and generally describes hormone-free and harmless methods for regulating conception or planning a pregnancy. NFP and the symptothermal method are often used as synonyms. In fact, the symptothermal method is only one of the methods that fall under NFP.
The symptothermal method is a non-invasive method that does not affect the hormonal balance. All that is needed to use the method is a basal thermometer that measures to two decimal places. The symptothermal method is used to determine the fertile days of the female cycle. Changes in basal body temperature and cervical mucus or the cervix are evaluated. The symptothermal method is a combination of the temperature method and the Billings method.