Ovulation & Fertility Calculator
Estimate ovulation and fertile window based on your cycle (for reference only).
Fill in the form and calculate.
What is Ovulation Calculator
Estimate the ovulation day, fertile window and next period from your last period start, cycle length, period length and luteal phase — using the rule that ovulation sits roughly one luteal phase before the next period. Upcoming cycles are previewed too, and everything computes locally on your device.
How to use Ovulation Calculator
- Enter your last period date, cycle length and luteal phase length
- Calculate to see the ovulation day and fertile window
- Scroll for the upcoming cycles forecast
Frequently asked questions
How reliable is the estimate?
It assumes a regular cycle and a typical luteal phase — real ovulation varies, so treat it as an approximation, not medical guidance.
What luteal phase length should I enter?
Most people are around 14 days (commonly 12–16). Leave it at 14 if unsure — a different value shifts the estimated ovulation day forward or back, and irregular cycles make any estimate less reliable.
Can this be used as contraception?
No — calendar-based "safe days" are unreliable because ovulation shifts with stress, sleep and illness, and sperm can survive 2–3 days. Use real contraception and consult a doctor for family planning.
Is my data stored or sent anywhere?
No — the local-only note is accurate: dates are processed in your browser and not uploaded.
Is Ovulation Calculator free?
Ovulation Calculator is completely free — open the page and use every feature with no hidden charges.
Do I need to download or install Ovulation Calculator?
No download or installation is needed. It is an online tool that runs in the browser on your phone, tablet and computer.
Do I need an account to use Ovulation Calculator?
No. Use the tool right away — no account or sign-in required.
Does Ovulation Calculator work on mobile?
Yes. The page is fully responsive and works on phones, tablets and desktop browsers.