Ovulation Calculator
Estimate your ovulation day and most fertile days from your last period and cycle length, with dates for the next three cycles.
Results
| Item | Value |
|---|
Next three cycles
| Cycle | Fertile window | Ovulation | Next period |
|---|
Quick Answer
Ovulation usually happens about 14 days before your next period. With a 28-day cycle that started on March 1, 2026, ovulation is around Sunday, March 15, 2026, and your fertile window is Mar 10 to Mar 15. The 2 to 3 days before ovulation and the day itself give the best chance of pregnancy.
Embed this calculator
Adjust the size if needed, then copy the code below into your page or blog. The calculator will load in an iframe and stay updated automatically.
Table of Contents
- Ovulation Calculator
- Quick Answer
- Related Calculators
- How This Ovulation Calculator Works
- How to Use the Ovulation Calculator
- Core Formulas
- Key Terms
- Worked Example
- Real-Life Examples
- Fertile Window vs Ovulation Day
- Ovulation Day by Cycle Length
- Signs of Ovulation
- Common Mistakes to Avoid
- Frequently Asked Questions
- References & Sources
How This Ovulation Calculator Works
Enter the first day of your last period and your usual cycle length. The calculator counts back from your next expected period by the length of the luteal phase, which is usually about 14 days, to estimate ovulation. Your fertile window is the 5 days before ovulation plus ovulation day, because sperm can live for several days.
Quick explanation: you can get pregnant from sex in the days before ovulation, not just on the day.
- Ovulation: about 10 to 16 days before your next period.
- Fertile window: about 6 days that end on ovulation day.
- Best days: the 2 days before ovulation and ovulation day.
How to Use the Ovulation Calculator
- Pick the first day of your last period.
- Enter your average cycle length, from the first day of one period to the first day of the next.
- Leave the luteal phase at 14 unless you know your own.
- Press Calculate.
- Read your ovulation day, fertile window and the dates for the next three cycles.
Core Formulas
- Ovulation day: first day of last period + (cycle length − luteal phase)
- Fertile window: 5 days before ovulation to ovulation day
- Next period: first day of last period + cycle length
- Due date if pregnant: first day of last period + 280 days + (cycle length − 28)
Key Terms
- Ovulation: the release of an egg from an ovary.
- Fertile window: the days in a cycle when sex can lead to pregnancy.
- Luteal phase: the time from ovulation to the next period, usually 10 to 16 days.
- Cycle length: days from the first day of one period to the first day of the next.
- LH surge: a rise in luteinizing hormone that triggers ovulation 1 to 2 days later.
Worked Example
Your last period started on March 1, 2026, and your cycles are 32 days long.
- Ovulation = March 1 + (32 − 14) days = Thursday, March 19, 2026
- Fertile window = Mar 14 to Mar 19
- Next period expected = Thursday, April 2, 2026
Real-Life Examples
- Trying to conceive: with a 28-day cycle from March 1, 2026, plan sex every 1 to 2 days from Mar 10 to Mar 15.
- Long cycles: a 32-day cycle moves ovulation to about Mar 19, 4 days later than a 28-day cycle.
- Short luteal phase: a 26-day cycle with a 12-day luteal phase gives ovulation on about Mar 15.
- Timing a test: wait until your period is due, around Mar 29 for a 28-day cycle, for the most reliable home test.
Fertile Window vs Ovulation Day
- Ovulation day: the day an egg is released. The egg lives about 12 to 24 hours.
- Fertile window: the days when sex can lead to pregnancy, because sperm can survive for several days.
- Why it matters: waiting until ovulation day can miss the best days, which come just before it.
Ovulation Day by Cycle Length
Day 1 is the first day of your period.
| Cycle length | Ovulation (cycle day) | Fertile window (cycle days) |
|---|---|---|
| 21 days | Day 7 | Days 2 to 7 |
| 24 days | Day 10 | Days 5 to 10 |
| 26 days | Day 12 | Days 7 to 12 |
| 28 days | Day 14 | Days 9 to 14 |
| 30 days | Day 16 | Days 11 to 16 |
| 32 days | Day 18 | Days 13 to 18 |
| 35 days | Day 21 | Days 16 to 21 |
Signs of Ovulation
- Cervical mucus: becomes clear, slippery and stretchy, like raw egg white.
- Ovulation tests: urine tests detect the LH surge 1 to 2 days before ovulation.
- Basal body temperature: rises slightly after ovulation.
- Other signs: some people feel a mild one-sided pain or notice breast tenderness.
Common Mistakes to Avoid
- Counting from the last day of your period. Cycle day 1 is the first day of bleeding.
- Assuming everyone ovulates on day 14. That only fits a 28-day cycle.
- Waiting for ovulation day. The days before it are just as important.
- Using it as birth control. Calendar dates alone are not reliable enough.
- Ignoring irregular cycles. If your cycle length changes a lot, use ovulation tests too.
Frequently Asked Questions
Usually about 14 days before your next period. With a 28-day cycle, that is around day 14.
About 6 days: the 5 days before ovulation and ovulation day.
The 2 days before ovulation and the day of ovulation.
Sperm can survive in the body for up to 7 days, according to the NHS, though most survive a shorter time.
About 12 to 24 hours.
It is possible, especially with short cycles, because sperm can live several days and ovulation may come early.
It gives an estimate based on averages. Ovulation tests and body signs can confirm the timing.
Use your shortest and longest cycles to see a range, and consider ovulation tests or a doctor visit.
No. Calendar estimates alone are not a reliable form of birth control.
Most home tests work best from the day your period is due.
21 to 35 days is normal for adults, according to the NHS. The average is about 28 days.
If you are under 35 and have tried for 12 months, or 35 or older and have tried for 6 months, or sooner if your periods are very irregular.
References & Sources
| Source | Used For | Link |
|---|---|---|
| NHS, Periods and fertility in the menstrual cycle | When ovulation happens and how long sperm live. | https://www.nhs.uk/conditions/periods/fertility-in-the-menstrual-cycle/ |
| ACOG, Fertility awareness-based methods of family planning | The menstrual cycle and fertile days. | https://www.acog.org/womens-health/faqs/fertility-awareness-based-methods-of-family-planning |