If you are trying to get pregnant, timing matters: you can only conceive during a few days of each cycle. This ovulation calculator predicts your ovulation day, your fertile window, your next period and when to take a pregnancy test, for the next six cycles.
Quick answer: Ovulation ≈ next period − 14 days (cycle day 14 in a 28-day cycle). The fertile window is the 5 days before ovulation through the day after. Last period October 1, 2026, 28-day cycle → ovulation about October 15, fertile window October 10–16, next period October 29.
How to use the ovulation calculator
- Enter the first day of your last period (the first day of full bleeding).
- Enter your average cycle length. Count from the first day of one period to the first day of the next and average the last 3–6 cycles.
- If you know your luteal phase from tracking, enter it; otherwise 14 days is used.
- Press Calculate to see your ovulation day, fertile window, most fertile days, next period and test date, plus a 6-cycle calendar.
Ovulation day by cycle length
| Cycle length | Ovulation (cycle day) | Fertile window (cycle days) |
|---|---|---|
| 21 days | Day 7 | 2–8 |
| 24 days | Day 10 | 5–11 |
| 26 days | Day 12 | 7–13 |
| 28 days | Day 14 | 9–15 |
| 30 days | Day 16 | 11–17 |
| 32 days | Day 18 | 13–19 |
| 35 days | Day 21 | 16–22 |
Based on a 14-day luteal phase. Day 1 is the first day of your period.
Example
Last period started October 1, 2026, cycle length 28 days:
- Next period: October 1 + 28 days = October 29
- Ovulation: October 29 − 14 days = Thursday, October 15
- Fertile window: October 10–16; most fertile: October 13–15
- Pregnancy test from: October 29
- Due date if you conceive this cycle: July 8, 2027
With a 32-day cycle, everything moves 4 days later: ovulation around October 19, next period November 2.
How to read your result
- It is an estimate. Ovulation can shift by a few days from cycle to cycle, especially with stress, illness or travel.
- Confirm with signs. A positive LH test, slippery cervical mucus and a rise in basal body temperature after ovulation help pinpoint the day.
- Once you conceive, use the due date calculator to estimate your due date and follow your pregnancy week by week.
- Weight affects fertility. Both underweight and obesity can disrupt ovulation; check your BMI and, if you want to change your weight, your daily needs with the calorie calculator.
- Counting cycle days? The age calculator also works as a days-between-dates counter.
Common mistakes
- Counting from the end of your period. Day 1 is the first day of bleeding.
- Assuming everyone ovulates on day 14. That only applies to 28-day cycles.
- Waiting until ovulation day. The days before ovulation are the most fertile.
- Using the calendar as contraception. It is not reliable for preventing pregnancy.
This calculator gives estimates for general information and is not medical advice. If you have been trying to conceive for 12 months (6 months if you are 35 or older), talk to your doctor.
Frequently asked questions
How do I calculate my ovulation day?
Ovulation usually happens about 14 days before your next period starts. Subtract 14 from your cycle length to find your ovulation day: with a 28-day cycle that is day 14, with a 32-day cycle day 18. If your last period started October 1, 2026 and your cycle is 28 days, you would likely ovulate around October 15.
What is the fertile window?
The fertile window is the 6 days when sex can lead to pregnancy: the 5 days before ovulation and ovulation day itself, plus the day after as a margin. Sperm can survive up to 5 days, while the egg lives for about 12–24 hours.
What are the most fertile days?
The two days before ovulation and the day of ovulation give the highest chance of pregnancy. For a 28-day cycle starting October 1, that is October 13–15.
Can I use an ovulation calculator with irregular periods?
A calendar estimate is less reliable when your cycle length varies by more than a few days. Enter your average cycle length, but consider ovulation predictor kits (LH strips) or tracking basal body temperature and cervical mucus for a more precise answer.
What is the luteal phase?
The luteal phase is the time from ovulation to your next period. It is fairly constant for each person, usually 12–16 days, and 14 on average. If you know yours from tracking, enter it for a more accurate prediction.
When should I take a pregnancy test?
Most home tests are accurate from the first day of your missed period. With a 28-day cycle that is about 14 days after ovulation. The calculator shows this date for you.
Can I get pregnant right after my period?
It is possible if you have a short cycle. With a 21-day cycle, ovulation can happen around day 7, so sex at the end of a period could fall inside the fertile window because sperm survive for several days.
Is an ovulation calculator a form of birth control?
No. Calendar predictions cannot account for the natural variation in ovulation from cycle to cycle, so they are not reliable for preventing pregnancy. Talk to your healthcare provider about contraception.
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