What you can expect

By Mayo Clinic Staff

To use the basal body temperature method:

  • Take your basal body temperature every morning before getting out of bed. Use a digital oral thermometer or one specifically designed to measure basal body temperature. Make sure you get at least six hours of uninterrupted sleep each night to ensure an accurate reading. You may consider taking your temperature vaginally or rectally if you have trouble determining a pattern or change in your basal body temperature. For the most accurate results, always take your temperature using the same method.
  • Plot your temperature readings on graph paper. Record your daily basal body temperature and look for a pattern to emerge. Your basal body temperature may increase slightly — typically less than 1 degree — when you ovulate. You can assume ovulation has occurred when the slightly higher temperature remains steady for three days or more.
  • Plan sex carefully during fertile days. You're most fertile during the two to three days before your basal body temperature rises, but sperm can live for up to five days in your reproductive tract. If you're hoping to get pregnant, this is the time to have sex. If you're hoping to avoid pregnancy, unprotected sex is off-limits from the start of your menstrual period until three to four days after your basal body temperature rises — every month.
Nov. 18, 2011