Table 1 Mean cycle lengths, bleed lengths, follicular phase lengths and luteal phase lengths in cohorts by cycle length

From: Real-world menstrual cycle characteristics of more than 600,000 menstrual cycles

Cycle length range in days Cycles (% of total) Mean ± std cycle length in days Mean ± std bleed length in days Mean ± std follicular phase length in days Mean ± std luteal phase length in days
15–20 3769 (<1%) 18.4 ± 1.6 3.5 ± 1.5 10.4 ± 2.4 8.0 ± 2.4
21–24 47,449 (8%) 23.4 ± 0.9 3.7 ± 1.4 12.4 ± 2.2 11.0 ± 2.2
25–30 395,631 (65%) 27.6 ± 1.6 3.9 ± 1.4 15.2 ± 2.5 12.4 ± 2.2
31–35 116,998 (19%) 32.4 ± 1.3 4.1 ± 1.5 19.5 ± 2.7 12.9 ± 2.3
36–50 43,240 (7%) 39.8 ± 3.7 4.2 ± 1.7 26.8 ± 4.5 12.9 ± 2.8
All cycles (10–90) 612,613 29.3 ± 5.2 4.0 ± 1.5 16.9 ± 5.3 12.4 ± 2.4