Ovulation & Fertility
Estimate your ovulation day and fertile window from the first day of your last period and your cycle length.
Results update as you type
Formulas use international (WHO) standards — healthy ranges are the same worldwide; only the units differ. The national context below uses U.S. data (CDC / NHANES).
How ovulation is estimated
The luteal phase (from ovulation to the next period) is fairly constant at about 14 days. So VitaDup estimates ovulation by subtracting 14 days from your next predicted period, based on your cycle length.
The fertile window spans the 5 days before ovulation plus ovulation day, because sperm can survive several days.
What to keep in mind
This is an estimate based on regular cycles. Stress, travel, weight changes or health conditions can shift ovulation earlier or later.
For more precision, combine it with body signals (basal temperature, cervical mucus) or ovulation tests.
Frequently asked questions
Can I use this as birth control?
Not reliably on its own. Calendar-based methods have a high failure rate; if you want to avoid pregnancy, ask about more effective options.
What if my cycle is irregular?
The estimate is less precise. Ovulation tests or basal temperature tracking are more useful then.
How often do I ovulate?
Once per cycle. The date shifts with your cycle length, which is why the calculator adjusts for it.
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This tool is for general education and is not a substitute for professional medical advice.