Ovulation Calculator

1. Enter the first day of your last menstrual period (LMP). This is Day 1 of your cycle, when bleeding begins. Do not use the last day of your period.
2. Set your typical cycle length. The average is 28 days, but normal cycles range from 21 to 45 days. If your cycles vary, use your average over the past 3-6 months. Shorter cycles mean earlier ovulation; longer cycles mean later ovulation.
3. Read the fertile window. The calculator estimates your ovulation date (typically 14 days before your next period) and marks the 6-day fertile window. The 2-3 days immediately before ovulation have the highest conception probability.

These are estimates based on average cycle patterns. Actual ovulation can vary by several days due to stress, illness, and other factors.

Ovulation day = LMP date + (cycle length - 14)

Fertile window: 5 days before ovulation
through 1 day after ovulation (6 days total)

Example: LMP = April 1, cycle = 28 days
Ovulation = April 1 + (28 - 14) = April 15
Fertile window = April 10-16

Conception probability by timing relative to ovulation: