Aava

Seasons by cycle length

How Aava splits each cycle into four seasons, for every length from 21 to 45 days. Day 1 is the first day of your period.

Scroll sideways to see all 45 days.

Faded rows (36 to 45 days) are outside the usual adult range of 21 to 35 days. In the first years after periods start, the usual range is 21 to 45 days.

How it is worked out

• Aava estimates ovulation as 14 days before the next period. Studies put the average luteal phase (the days after ovulation) at about 12 to 14 days.
• Summer is the estimated day of ovulation and two days either side. This is Aava's own definition.
• Cycle length varies mostly before ovulation, so a longer cycle has a longer spring and the other seasons stay about the same.
• In very short cycles, ovulation is placed later so that spring is never skipped, and autumn is shorter.
• Actual timing varies between cycles and between people.

Sources

• Lenton EA, et al. Normal variation in the length of the luteal phase of the menstrual cycle: identification of the short luteal phase. Br J Obstet Gynaecol. 1984;91(7):685–689. Link
• Bull JR, et al. Real-world menstrual cycle characteristics of more than 600,000 menstrual cycles. npj Digit Med. 2019;2:83. Link
• American College of Obstetricians and Gynecologists. Abnormal Uterine Bleeding (patient FAQ). Link
• ACOG Committee Opinion No. 651. Menstruation in Girls and Adolescents: Using the Menstrual Cycle as a Vital Sign. Obstet Gynecol. 2015;126(6):e143–e146. Reaffirmed 2025. Link