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ARVENRA
Pregnancy & reproductive health

Ovulation Calculator

Estimated ovulation and the fertile window across upcoming cycles.

Ovulation is counted back from the next period rather than forward from the last. The reason is that the luteal phase — from ovulation to the next period — is relatively stable, while total cycle length varies more.

Your details

From the first day of one period to the first day of the next. Default 28 days.

Typical range: 20 – 45

From ovulation to the next period — typically about 14 days and fairly stable.

Typical range: 9 – 18

Typical range: 1 – 12

The values you enter are calculated in your browser only — nothing is stored or transmitted.

Fill in your details and press calculate — your result will appear here.

Formula and method

The ovulation day is cycle length minus luteal phase length. The fertile window runs five days before it to one day after.

Formula used

Ovulation = cycle length - luteal phase; six-day fertile window

Assumptions and limits

  • This works for regular cycles. If yours is irregular, accuracy drops sharply.
  • This tool is not a method of contraception.

Scientific sources

  1. Wilcox AJ, Weinberg CR, Baird DD. “Timing of sexual intercourse in relation to ovulation.” N Engl J Med. 1995;333(23):1517-1521.

    View source

  2. American College of Obstetricians and Gynecologists. “Committee Opinion No. 651: Menstruation in Girls and Adolescents.” Obstet Gynecol. 2015;126(6):e143-e146.

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