Typically 14 days before your next period. In a 28-day cycle, ovulation is around day 14. In a 30-day cycle, around day 16. The luteal phase (post-ovulation) is consistently ~14 days.

When are my most fertile days?

The 3 peak days are: 2 days before ovulation, 1 day before, and ovulation day. Conception is most likely with intercourse on these 3 days. The day before ovulation has the highest probability.

How accurate is an ovulation calculator?

Based on averages, not your actual hormones. Accuracy depends on cycle regularity. For irregular cycles, use ovulation predictor kits (OPKs) or basal body temperature tracking for confirmation.

Can I get pregnant outside my fertile window?

Extremely unlikely. The egg survives only 12-24 hours after ovulation. Sperm survive up to 5 days. Outside this 6-day window, conception is virtually impossible. However, cycle prediction is not perfect.

What is an ovulation predictor kit (OPK)?

A urine test that detects the LH surge 24-36 hours before ovulation. More accurate than calendar prediction. Start testing 3-4 days before expected ovulation. A positive means ovulation is imminent.

Ovulation Calculator - Free Ovulation & Fertility Tracker (2026)

Your Ovulation Prediction

Based on your cycle length and last period

Ovulation Day

Apr 17

Fertile Window

Apr 12 - 18

Next Period

May 1

Days to Ov

3 days

Your Cycle Map

Day 1 (Period)Fertile WindowOvulationNext Period

Next 4 Cycles Predicted

Cycle	Period Start	Ovulation	Fertile Window	Next Period

// Health · ShashaTools

Ovulation Calculator

First Day of Last Period

The first day of your most recent menstrual period.

Average Cycle Length

Average days from period start to next period start. 28 is standard. Count from day 1 of one period to day 1 of the next.

Period Duration (days)

How many days your period typically lasts.

// Results

Ovulation Date

Apr 17

Ovulation

Apr 17 (Thu) — Day 14

Fertile Window

Apr 12 – Apr 18 (6 days)

Peak Fertility

Apr 15 – Apr 17 (3 days)

Next Period

May 1 (Thu)

Cycle Day

Day 14 of 28-day cycle

Ovulation: Apr 17. Fertile: Apr 12 - 18

How to Use This Calculator

Predict ovulation and your fertile window

Step 1 Enter Your Cycle

Enter last period date

The first day of your most recent period. This is day 1 of your current cycle.

Set cycle length

Average days between periods (day 1 to day 1). Count from your last 3-6 cycles and average. 28 is standard but 24-35 is normal.

Set period duration

How many days your period lasts. Used for the cycle visualization bar. Typical: 3-7 days.

Read your predictions

Ovulation day, 6-day fertile window, 3-day peak fertility, and next period date. The table shows the next 4 cycles.

💡 Key rule: Ovulation occurs ~14 days BEFORE your next period (not 14 days after your last). The luteal phase is consistently 14 days. The follicular phase (before ovulation) varies with cycle length.

Step 2 Maximize Accuracy

Confirm with OPK tests

Ovulation predictor kits detect the LH surge 24-36 hours before ovulation. Start testing 3-4 days before your predicted date for confirmation.

Track basal body temp

BBT rises 0.2-0.5°F after ovulation and stays elevated. Track daily with a basal thermometer before getting out of bed. Confirms ovulation after the fact.

Watch cervical mucus

Becomes clear, stretchy, and egg-white consistency near ovulation. This is the most fertile mucus type. Dry or sticky = less fertile.

Time intercourse

For conception: every 1-2 days during the fertile window, especially the 3 peak days. The day before ovulation has the highest success rate.

💡 Tip: This calculator gives predictions, not certainties. Stress, illness, travel, and weight changes can shift ovulation. For the most reliable tracking, combine calendar prediction with OPK testing and BBT tracking.

// Recommended Fertility Tools

ℹ️ Affiliate disclosure: Some links are affiliate links.

Ovulation Test Strips

Detect LH surge 24-36 hours before ovulation.

Compare →

Basal Thermometer

Track BBT to confirm ovulation each cycle.

Shop →

Fertility Tracker

Wearable fertility monitors with app tracking.

Compare →

Prenatal Vitamins

Start prenatal vitamins when trying to conceive.

Shop →

// Related Calculators

📅

Pregnancy Due Date Calculator

Find your due date once pregnant.

🥗

Macros for Pregnancy

Nutrition targets by trimester.

⚖️

BMI Calculator

Healthy BMI supports fertility.

💧

Water Intake Calculator

Hydration supports reproductive health.

// Complete Guide — Updated 2026

Understanding Ovulation:
The Complete Guide

Ovulation is the release of an egg from the ovary. It happens once per cycle and creates a brief window when pregnancy is possible. Understanding when you ovulate is essential whether you are trying to conceive or trying to avoid it. This guide explains the science behind ovulation, how to predict it, and how to maximize your chances of conception.

The Ovulation Formula

// Ovulation Day

Ovulation = Cycle Length − 14 days

28-day cycle: ovulation on day 14. 32-day cycle: day 18. 24-day cycle: day 10.

Real-World Scenarios

Scenario 1: Trying to Conceive (28-day cycle). Maria has a regular 28-day cycle. LMP: April 3. Ovulation: April 17 (day 14). Fertile window: April 12-18. Peak days: April 15-17. She and her partner have intercourse every other day from April 12-18. The day before ovulation (April 16) has the highest conception probability at ~33%. Use our Due Date Calculator if conception occurs.

Scenario 2: Irregular Cycles. Sarah has cycles ranging from 26-34 days. Average: 30 days. Predicted ovulation: day 16. But actual ovulation could range from day 12-20. She uses OPK test strips starting day 10 to catch the actual LH surge. The calculator gives a starting point; OPKs give confirmation.

Scenario 3: Short Cycle. Priya has a 24-day cycle. Ovulation: day 10. Fertile window starts day 5 — just as her period ends (5-day period). She could theoretically conceive from intercourse during the last day of her period. Short cycles mean the fertile window starts very early.

Scenario 4: Long Cycle. Lisa has a 35-day cycle. Ovulation: day 21. Her fertile window is days 16-22. If she assumed ovulation on day 14 (standard advice), she would miss her actual fertile window by a full week. Cycle length matters. Always calculate from YOUR cycle, not the textbook 28 days.

💡 Key insight: The day before ovulation has the highest conception probability (~33%). Ovulation day itself is only ~15% because the egg has already started aging. Sperm need to be waiting for the egg, not chasing it. Time intercourse for 1-2 days before predicted ovulation for the best chance.

Ovulation Signs

Cervical mucus	Clear, stretchy
BBT rise	+0.2-0.5°F
OPK test	Positive (LH surge)
Pelvic pain	Mild (mittelschmerz)
Libido	Increased

// Frequently Asked Questions

Common Questions About Ovulation

When do I ovulate? +

~14 days before your next period. 28-day cycle: day 14. 30-day: day 16. The luteal phase is consistently ~14 days. The follicular phase varies.

What is the fertile window? +

6 days: 5 before ovulation + ovulation day. Sperm survive up to 5 days. The egg lives 12-24 hours. This overlap creates the fertile window.

When am I most fertile? +

Peak: 2 days before ovulation, 1 day before, and ovulation day. The day BEFORE ovulation has the highest conception rate (~33%).

How accurate is this calculator? +

Based on averages, not hormones. Accuracy depends on cycle regularity. For irregular cycles, confirm with OPK tests or BBT tracking.

How do I know if I am ovulating? +

Signs: egg-white cervical mucus, BBT rise, positive OPK, mild pelvic pain, increased libido. Combination of signs is most reliable.

Can I conceive outside the fertile window? +

Extremely unlikely. Egg survives 12-24 hours, sperm up to 5 days. Outside the 6-day window, conception is virtually impossible.

What if my cycle is irregular? +

Average last 3-6 cycles. For highly irregular (7+ day variation), use OPK tests starting day 10 to detect actual LH surge.

How does cycle length affect ovulation? +

Longer cycles delay ovulation. 35-day cycle: ovulation day 21. 24-day: day 10. Always calculate from YOUR cycle length, not the standard 28.

What is an OPK? +

Ovulation predictor kit — urine test detecting LH surge 24-36 hours before ovulation. More accurate than calendar. Start testing 3-4 days before expected ovulation.

Can stress affect ovulation? +

Yes. Stress, illness, travel, weight changes, and excessive exercise can delay or suppress ovulation. Calendar tracking alone is not 100% reliable.

OvulationCalculator

Understanding Ovulation:The Complete Guide

The Ovulation Formula

Real-World Scenarios

Ovulation
Calculator

Understanding Ovulation:
The Complete Guide