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Ovulation Calculator

Predict your next ovulation day, fertile window, next period, and luteal phase from your last menstrual period and cycle length, with multi-cycle forecasts.

Last updated: 2026/10/16 Calculator Feedback & bug reports
This tool calculates a general estimate assuming a regular cycle. It is not medical advice, nor a method of contraception or a reliable way to confirm pregnancy. Always consult your doctor about conception and your health.
Input
Enter the first day of your most recent period.
days
Days from one period start to the next. The standard is 28 days.
days
Days from ovulation to the next period. Usually about 14 days.
cycles
How many cycles ahead to forecast (1–12).
Enter your last menstrual period to see your next ovulation day and fertile window.

How to Use

1

Enter your last menstrual period

Pick the first day of your most recent period from the calendar. Use the "Today" button to quickly enter the current date.

2

Adjust cycle and luteal phase (optional)

If your cycle differs from 28 days, enter the actual length. If you know your luteal (high-temperature) phase from charting basal body temperature, adjust it for more accuracy.

3

Review ovulation and fertile window

See your next ovulation day, fertile window, next period date, and luteal phase. The cycle-by-cycle table lets you plan several cycles ahead.

About the Ovulation Calculator

A web tool that predicts your next ovulation day, fertile window, next period date, and luteal (high-temperature) phase from your last menstrual period (LMP) and cycle length. Ovulation is estimated as roughly 14 days before your next period, and the fertile window spans from five days before ovulation to the day after, accounting for sperm survival. Forecasts for multiple cycles are shown together so you can plan ahead for conception or scheduling. All calculations run entirely in your browser, so the dates you enter are never sent to any server. This tool provides a general estimate only and is not a substitute for medical advice or contraception.

Features

  • Real-time CalculationEnter a date or cycle length and instantly see ovulation and the fertile window. No buttons to press.
  • Multi-cycle ForecastView ovulation, fertile windows, and period start dates for up to 12 cycles ahead in one list.
  • Luteal Phase AwareAdjust the luteal (high-temperature) phase length to combine with your basal body temperature records.
  • Privacy ProtectedAll processing happens in your browser. The data you enter is never sent to servers.

Use Cases

  • Identify your fertile window for trying to conceive
  • Know your next ovulation and period dates in advance
  • Check your luteal phase alongside basal body temperature records
  • Plan trips and events around your menstrual cycle
  • Anticipate cycle-related changes in how you feel

FAQ

How is the ovulation day calculated?
Ovulation is estimated as roughly 14 days before your next expected period. Specifically, it is your last menstrual period plus (cycle length − luteal phase length, default 14 days). With a 28-day cycle and a 14-day luteal phase, ovulation falls about 14 days after the first day of your period.
What is the fertile window?
Sperm can survive up to about five days inside the body, and an egg lives roughly one day after ovulation. So the fertile window spans about six days—from five days before ovulation to the day after. The ovulation day and the day before it are considered the most fertile.
Can I use it with an irregular cycle?
You can, but the tool assumes a regular cycle, so predictions are less accurate for irregular cycles. Entering the average length of your recent cycles gives a useful estimate. For precise ovulation tracking, basal body temperature, ovulation tests, or a doctor's exam are helpful.
Should I change the luteal phase length?
The luteal phase (from ovulation to the next period) is about 14 days for most people but varies between roughly 10 and 16 days. If you know your own luteal phase from basal body temperature charting, entering it makes the ovulation prediction more realistic. If unsure, leaving the default of 14 days is fine.
Can I use this tool for contraception?
No. This tool only provides an estimate and cannot be used as a method of contraception. Ovulation can shift due to health, stress, and other factors, and pregnancy is not impossible outside the predicted fertile window. Consult your doctor about appropriate contraception.
Are the dates I enter saved?
No. All calculations happen entirely in your browser, and the dates you enter are never sent to or stored on any server, so you can use the tool with peace of mind.

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