📅Ovulation Calculator
Estimate your ovulation date and fertile window to increase your chances of getting pregnant
Last updated: January 4, 2026
How to Calculate Ovulation and Due Date
Our ovulation calculator (also known as a fertility calculator) uses the standard medical rhythm method to predict your most fertile days. Understanding your cycle is key to using an ovulation tracker effectively.
To answer "when am I ovulating?", we look at your menstrual cycle. A typical cycle lasts 28 days, but anything from 21 to 35 days is normal.
The Science and Formulas
Ovulation typically occurs about 14 days before your next period starts.
Ovulation Date = (Last Period Date + Cycle Length) - 14 days
Your fertility window includes the days sperm can survive inside the body (up to 5 days) plus the day the egg is released.
Fertile Window = 5 days before Ovulation + Day of Ovulation
Fertile Days Calculator Table
Below is a general guide to the fertility window for a standard 28-day cycle:
| Cycle Day | Fertility Status | Probability of Conception |
|---|---|---|
| Day 1-7 | Menstruation | Very Low |
| Day 8-9 | Pre-Fertile | Low |
| Day 10-14 | Fertile Window | High |
| Day 14 | Ovulation | Peak Fertility |
| Day 15-28 | Luteal Phase | Low |
*Note: This table assumes a 28-day cycle. Use our free ovulation calculator above for your specific dates.*
How to Use the Ovulation Calculator
Tracking your cycle is easy with this tool. Just follow these steps:
- Enter the First Day of Your Last Period: Click on the date picker and select the date.
- Enter Your Average Cycle Length: The default is 28 days, but adjust it to match your personal cycle.
- View Your Results: The calculator will instantly display your Estimated Ovulation Date, Fertile Window, Next Period Start, and Pregnancy Test Date.
Use these dates to plan intercourse if you are trying to conceive.
Accuracy Factors
This ovulation calculator based on last period provides an estimate. Factors including stress, illness, medications, or conditions like PCOS can affect cycle length. For precise tracking, combine this menstrual cycle calculator with ovulation predictor kits or basal body temperature monitoring.
Frequently Asked Questions
You are most fertile during the 2-3 days leading up to and including the day of ovulation. This calculator gives you a wider "fertile window" to ensure you cover the entire possible timeframe.
This calendar provides estimates based on averages. If you have a regular cycle, it can be very accurate. However, if your cycle is irregular, the results may vary. It works best as a general guide.
It is highly unlikely. Pregnancy requires an egg and sperm to meet. Since the egg only survives for up to 24 hours and sperm for up to 5 days, conception generally only occurs within this ~6 day window around ovulation.
A normal menstrual cycle can range from 21 to 35 days. The average is 28 days.