Ovulation Calculator 2026 — Free Online Tool

Calculate fertile window, peak ovulation date & pregnancy due date.

Quick Answer

Ovulation typically occurs 14 days before your next period begins. Your fertile window spans the 5 days leading up to ovulation plus ovulation day itself (a 6-day fertile window).

Medical Disclaimer (Estimate Only): This calculator provides mathematical estimates based on standard cycle lengths and should not be used as a method of contraception or medical diagnosis. For health decisions, this is an estimate only — consult a doctor or qualified healthcare provider for personalized medical guidance.

Enter Cycle Information

First Day of Last Period (LMP)Average Cycle Length (28 days)

21 days28 days35 days

Normal range: 21 to 35 days (default 28)

Estimated Ovulation Date

Wed, Nov 4, 2026

~0 days from today

Peak Fertile Window

Fri, Oct 30, 2026 – Thu, Nov 5, 2026

Highest chance of conception

Next Expected Period

Wed, Nov 18, 2026

~14 days away

Conception & Pregnancy Due Date Estimator (Naegele's Rule)

If conception occurs during this cycle, here is your estimated pregnancy due date and milestone timeline based on 280 days (40 weeks) from your LMP:

Estimated Due Date

Wed, Jul 28, 2027

40 weeks from LMP

1st Trimester End

Wed, Jan 13, 2027

End of Week 12

2nd Trimester End

Wed, Apr 28, 2027

End of Week 27

Medical Disclaimer: This calculator provides mathematical estimates only and is not a substitute for professional medical advice, diagnosis, or contraception. Ovulation and fertility windows vary with cycle irregularities, stress, and health conditions. Always consult a qualified doctor or healthcare specialist for personal medical and reproductive guidance.

How to Use This Tool

Select the first day of your Last Menstrual Period (LMP).
Adjust your average menstrual cycle length (default is 28 days, normal range 21 to 35 days).
View your estimated peak ovulation date, 6-day fertile window, and next period start date.
Check the bonus Pregnancy Due Date (Naegele's Rule: 280 days) if conception occurs during this cycle.

Formula & Specifications

Ovulation Day = LMP + Cycle Length - 14 Days | Fertile Window = Ovulation Day - 5 Days to Ovulation Day + 1 Day | Due Date = LMP + 280 Days

About Ovulation Calculator

Calculate your peak fertile days, ovulation date, next menstrual period, and estimated pregnancy due date. Essential free tool for fertility planning, pregnancy tracking, and natural family planning. Uses the Naegele's Rule standard for due date estimation and Ogino-Knaus method for ovulation day calculation.

Frequently Asked Questions

When does ovulation occur in a typical menstrual cycle?

Ovulation typically occurs approximately 14 days before the start of your next menstrual period. For a standard 28-day cycle, ovulation happens around day 14. For shorter cycles (e.g., 24 days), ovulation occurs around day 10, and for longer cycles (e.g., 35 days), it occurs around day 21. This calculator uses the Naegele's Rule-based method to estimate your ovulation date.

What is the fertile window and how long does it last?

The fertile window is the period during which conception is possible. It spans from 5 days before ovulation (because sperm can survive 3–5 days in the female reproductive tract) through the day of ovulation itself (the egg survives 12–24 hours). This gives a maximum fertile window of approximately 6 days per cycle.

How accurate is an ovulation calculator?

Ovulation calculators provide estimates based on average cycle patterns. They are most accurate for women with regular, consistent cycle lengths. Factors like stress, illness, travel, hormonal changes, or PCOS can shift ovulation. For precise ovulation tracking, consider using ovulation predictor kits (OPKs), basal body temperature (BBT) charting, or consulting a fertility specialist.

What is Naegele's Rule for estimating a pregnancy due date?

Naegele's Rule estimates the expected due date (EDD) by adding 280 days (40 weeks) to the first day of the Last Menstrual Period (LMP). This is equivalent to adding 9 months and 7 days. The rule assumes a regular 28-day cycle with ovulation on day 14. Our calculator uses this standard obstetric method to estimate your due date if conception occurs this cycle.