You will need to know the length of your menstrual cycle. To figure it out, track your menstrual cycle for several months. A menstrual cycle:
- Starts with the first day your period starts.
- Ends the day before your next period starts.
- The average length is 28 days.
This tool is only an estimate and does not work for menstrual cycles that are shorter than 27 days or longer than 29 days. Do not use this if you have not had a period in the last 29 days. It also does not work if your menstrual cycle is irregular from month to month.
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Sources: Levine JP, Mravcak S, Wu J. Contraception. In: Rakel RR, ed. Textbook of Family Medicine. 7th ed. Philadelphia, PA; Saunders Elselvier; 2007: 689-702. This calculator is for adults and is provided for your information only. It is not a substitute for professional medical advice, and may not represent your individual medical situation. Other methods of determining fertility use basal body temperature and other evidence of ovulation and are considered to be more accurate than the calendar method. Ask your doctor for more information. |
