Ovulation Calculator
Find your ovulation day, fertile window and next period over three cycles
Your cycle
Days from ovulation to your next period. 14 is the average; leave it unless you track it.
Your fertile days
Enter the first day of your last period to see your fertile window.
Frequently asked questions
How do I calculate my ovulation day?
Take the date your next period is due and subtract your luteal phase, which is about 14 days for most people. With a 28 day cycle that lands on day 14; with a 32 day cycle it is around day 18. This calculator does that for you from your last period and cycle length.
What is the fertile window?
The six days ending one day after ovulation: the five days before it, ovulation day and the day after. Sperm can survive up to five days in the reproductive tract, so sex in the days before ovulation can still lead to pregnancy. The two days before ovulation and ovulation day itself carry the highest chance.
Can I use an ovulation calculator as birth control?
No. It estimates ovulation from averages, and ovulation can move by several days because of stress, illness, travel or an irregular cycle. Calendar methods alone have a high failure rate, so use a reliable contraceptive if you want to avoid pregnancy.
When should I take a pregnancy test?
From the day your period is due, which is about 14 days after ovulation. Testing earlier often gives a false negative because hCG levels are still too low to detect.
Does it work with irregular cycles?
It is less accurate, because it assumes every cycle has the same length. If your cycles vary, use your shortest cycle to find the earliest fertile day and your longest for the latest, or confirm ovulation with LH test strips or basal body temperature.