Fertile Window Calculator: Find Your Most Fertile Days to Conceive
Free fertile window calculator to find when you are most fertile. Enter your last period date and cycle length to instantly see your ovulation day and best days to conceive. Our ovulation calculator displays a visual monthly fertility calendar with your complete fertile window highlighted.
Calendar Settings
Calendar Legend
February 2026
Enter your last period date to generate your fertility calendar
Frequently Asked Questions
How many days each cycle am I fertile?
Most women are fertile for about 6 days each cycle. This includes the 5 days before ovulation (when sperm can survive in the reproductive tract) plus the day of ovulation itself. However, the 2-3 days leading up to and including ovulation represent your peak fertility period when conception is most likely to occur. The exact timing depends on your individual cycle length and ovulation patterns.
Can I export my fertile days to a calendar?
Yes! Our calendar tool allows you to export your fertile days in two formats. You can download a CSV file that opens in Excel or Google Sheets for tracking and analysis, or export an ICS calendar file that you can import directly into Google Calendar, Outlook, Apple Calendar, or any other calendar application. This makes it easy to keep track of your fertile windows alongside your other appointments and plans.
Medical Disclaimer
This fertility calendar provides estimates based on average cycle patterns and should not be used as the sole method for family planning or contraception. Individual cycles vary, and many factors can affect ovulation timing. For medical advice or concerns about fertility, please consult with a qualified healthcare provider.
How to Use This Calculator
Follow these simple steps to generate your personalized fertile window calendar:
- Enter your last period start date -- Select the first day of your most recent menstrual period from the date picker in the Calendar Settings panel on the left.
- Set your average cycle length -- Choose the number of days between the start of one period and the start of the next. If you are unsure, 28 days is a common default.
- Set your period length -- Select how many days your period typically lasts. The average is 5 days.
- Review the color-coded calendar -- Your fertile window, ovulation day, menstrual phase, follicular phase, and luteal phase are highlighted automatically for the displayed month.
- Navigate between months -- Use the left and right arrows above the calendar to view future or past months.
- Export your data -- Click "Export Calendar" to download a CSV file for spreadsheets or an ICS file for your calendar app.
Understanding the Fertile Window
What Is the Fertile Window?
The fertile window is the span of days in each menstrual cycle during which intercourse can lead to pregnancy. It encompasses the five days leading up to ovulation plus the day of ovulation itself, resulting in approximately six fertile days per cycle. The reason the window extends before ovulation is that sperm can survive in the female reproductive tract for up to five days, waiting to fertilize the egg once it is released.
How Long Does the Fertile Window Last?
The fertile window lasts about six days in total, but the probability of conception is not equal across those days. The highest chances of pregnancy occur during the two to three days immediately before ovulation and on ovulation day itself. After the egg is released, it remains viable for only 12 to 24 hours. If fertilization does not occur within that narrow timeframe, the egg disintegrates and is absorbed by the body.
How to Identify Your Fertile Window
Several methods can help you pinpoint your fertile days. Calendar-based tracking, like this tool, estimates ovulation by counting backward 14 days from your expected next period. Ovulation predictor kits (OPKs) detect the surge in luteinizing hormone that precedes egg release by 24 to 36 hours. Basal body temperature (BBT) charting reveals a slight rise of 0.2 to 0.5 degrees Fahrenheit after ovulation has occurred. Monitoring cervical mucus is another approach -- fertile-quality mucus is clear, slippery, and stretchy, resembling raw egg whites.
Factors That Affect Fertility
Many variables influence the timing and viability of the fertile window. Irregular cycle lengths make it harder to predict ovulation with calendar methods alone. Stress, significant weight changes, intense exercise, and illness can all shift ovulation earlier or later in the cycle. Age plays a role as well -- egg quality and quantity decline over time, particularly after age 35. Certain medical conditions such as polycystic ovary syndrome (PCOS), thyroid disorders, and endometriosis can also affect ovulation regularity and overall fertility.
Estimated Ovulation Day by Cycle Length
The table below shows the approximate ovulation day for common cycle lengths, calculated by subtracting 14 days from the total cycle length.
| Cycle Length | Estimated Ovulation Day | Fertile Window (Approx.) |
|---|---|---|
| 21 days | Day 7 | Days 2 - 8 |
| 24 days | Day 10 | Days 5 - 11 |
| 26 days | Day 12 | Days 7 - 13 |
| 28 days | Day 14 | Days 9 - 15 |
| 30 days | Day 16 | Days 11 - 17 |
| 32 days | Day 18 | Days 13 - 19 |
| 35 days | Day 21 | Days 16 - 22 |
Important Disclaimer
This fertile window calendar provides estimates based on standard cycle calculations and should not replace professional medical guidance. Ovulation timing varies between individuals and can shift from cycle to cycle. This tool should not be relied upon as a method of contraception. If you are actively trying to conceive or have concerns about your fertility, consult a qualified healthcare provider for personalized evaluation and advice.
When Am I Most Fertile?
Understanding when you are most fertile is the key to successful conception planning. Our fertile window calculator estimates your 6-day fertile window based on your menstrual cycle length. The fertile window includes the 5 days before ovulation (because sperm can survive up to 5 days in the reproductive tract) plus ovulation day itself.
Research published in the New England Journal of Medicine shows that the probability of conception is highest when intercourse occurs 1-2 days before ovulation, not on ovulation day itself. This is because the egg survives only 12-24 hours after release, while sperm can remain viable for up to 5 days. Our ovulation calculator highlights these peak fertility days on your calendar.
For the most accurate results, combine this fertility calendar with other ovulation tracking methods: ovulation predictor kits (OPKs), basal body temperature (BBT) charting, and cervical mucus observation. If your cycles are irregular (varying by more than 7 days month to month), consider using our Ovulation Calculator for Irregular Cycles for a more tailored estimate.