Health & Fitness
Ovulation Calculator
Estimate ovulation date and fertile window based on cycle length.
Formulas and edge cases are reviewed against authoritative references before publication. For methodology, editorial standards, or corrections, use the links below.
Frequently asked questions
How is ovulation estimated?
Ovulation is estimated as 14 days before the next period.
What is the fertile window?
The fertile window includes the days leading up to and just after ovulation.
Is this accurate for irregular cycles?
Accuracy may be lower for irregular cycles.
Related tools
About this tool
Inputs
- First day of last period
- Cycle length
Results
- Ovulation date
- Fertile start
- Fertile end
If you have ever wondered how the numbers add up, this Ovulation Calculator shows you. Enter your figures and the result appears immediately. Enter first day of last period and cycle length. The tool processes your data and returns ovulation date, fertile start and fertile end. Body composition, metabolism, and vital signs interact in complex ways that a single number cannot capture.
BMI divides weight in kilograms by the square of height in meters (kg/m²). Whether you need to estimate ovulation date and fertile window based on cycle length for a quick check or a thorough analysis, this tool adapts to both. Use results as a conversation starter with a healthcare professional, not as a substitute for medical advice. The fertile window includes the days leading up to and just after ovulation. Run the calculation with your best-case and worst-case assumptions to bracket the likely outcome.