Free tools Ovulation Calculator
Free tool · trying to conceive
Ovulation Calculator: Your Fertile Days and Best Days to Get Pregnant
See your fertile window, your likely ovulation day, the best days to try, when your next period is due and the earliest day for a pregnancy test, for the next six cycles, on a simple calendar. Nothing you type leaves your phone.
Important: NOT birth control, and not medical advice.
- This is NOT a method of contraception or birth control. Do not use it to avoid pregnancy.
- For general information and education only: not medical advice, diagnosis or treatment. Dates are estimates and may be wrong for your cycle.
- Do not use it to make medical, fertility or contraception decisions. Always ask a qualified doctor or gynaecologist.
- Emergency? Severe pain or very heavy bleeding: contact a doctor or hospital right away.
Parent Oven accepts no liability for decisions made using this tool. Last reviewed: 31 Oct 2026 · Sources
Cycle length is from the first day of one period to the first day of the next. If it changes, use your average of the last few months.
Advanced: luteal phase
Most people have 12 to 14 days. Leave it at 14 unless you have tracked ovulation with tests or temperature.
Nothing you type is saved or sent anywhere. It all stays on your phone.
How to use it
- Enter the first day of your last period (the first day of real bleeding, not spotting).
- Choose your usual cycle length: the number of days from the first day of one period to the first day of the next. If it varies, use the average of your last 3 to 6 cycles.
- Optional: if you have tracked ovulation with tests or temperature and know your luteal phase (ovulation to next period), set it under Advanced. Otherwise leave it at 14.
- Tap Show my fertile days. Use the arrows on the calendar to move between months, and Add to my calendar to save your fertile windows on your phone.
How the calculator works
Ovulation happens a fairly fixed time before the next period, usually about 12 to 14 days. So the calculator counts back from your next expected period. Your next period is due on the last period date + your cycle length, and ovulation is on cycle day (cycle length − 14): day 14 of a 28-day cycle, day 18 of a 32-day cycle. If you set your own luteal phase under Advanced, it uses that number instead of 14.
Your fertile window is the 6 days ending on ovulation day. An egg lives for about a day, but sperm can survive up to 5 days, so sex in the 5 days before ovulation can still lead to pregnancy. In the well-known study by Wilcox and colleagues (NEJM, 1995), pregnancies happened only when sex was in this 6-day window, and the chance was highest in the 2 days before ovulation and on the day itself. Those 3 days are marked as most fertile.
| Your cycle | Likely ovulation | Fertile window |
|---|---|---|
| 24 days | Day 10 | Days 5 to 10 |
| 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 |
Day 1 is the first day of your period. The table assumes a 14-day luteal phase.
Why the calendar is only a guide
Even with regular periods, ovulation moves around from one cycle to the next. A later study (BMJ, 2000) found that the fertile window fell fully between days 10 and 17 of the cycle in only about 30% of women. Stress, illness, travel, breastfeeding and conditions such as PCOS can all shift it. To narrow down your own days, combine the calendar with body signs:
- Ovulation (LH) test strips from a chemist: a positive test means ovulation is likely in the next 1 to 2 days.
- Cervical mucus: in the fertile days it becomes clear, slippery and stretchy, like raw egg white.
- Basal body temperature: a small rise (about 0.2 to 0.5 °C) after ovulation. It confirms ovulation has happened, so it helps you learn your pattern over a few months.
The simplest advice from the NHS: have sex every 2 to 3 days through the whole cycle, and you do not need to time it exactly.
When to see a doctor
- You are under 35 and have been trying for 12 months, or you are 35 or over and have been trying for 6 months (ACOG).
- Your cycles are usually shorter than 24 days or longer than 38 days, or change by more than a week from month to month. These are outside the normal range set by FIGO and can mean you are not ovulating every month.
- Your periods have stopped, are very heavy or very painful, or you bleed between periods or after sex.
- You have a known condition such as PCOS, endometriosis or thyroid problems, or your partner has a known fertility issue.
This calculator gives estimates for information only. It is not medical advice and is <strong>not a method of birth control</strong>; calendar methods alone are much less reliable than contraception (<a href=”https://www.acog.org/womens-health/faqs/fertility-awareness-based-methods-of-family-planning” target=”_blank” rel=”noopener”>ACOG on fertility awareness methods</a>).
Sources
Official and primary sources only. Links were checked on 31 October 2026; any we could not open are marked.
- New England Journal of Medicine (primary study). Wilcox AJ, Weinberg CR, Baird DD. Timing of sexual intercourse in relation to ovulation (1995). Used for: the 6-day fertile window ending on ovulation day (N Engl J Med 1995;333:1517–21). Note: link goes to the PubMed record of the paper.
- BMJ (primary study). Wilcox AJ, Dunson D, Baird DD. The timing of the “fertile window” in the menstrual cycle (2000). Used for: how much ovulation day varies, even in regular cycles (BMJ 2000;321:1259–62). Note: link goes to the PubMed record of the paper.
- International Federation of Gynecology and Obstetrics (FIGO). Munro MG et al. The two FIGO systems for normal and abnormal uterine bleeding symptoms (2018). Used for: the normal cycle length range of 24 to 38 days used for the irregular-cycle warning (Int J Gynaecol Obstet 2018;143:393–408). Note: link goes to the PubMed record of the paper.
- NHS (UK). Trying to get pregnant (web page, checked Oct 2026). Used for: ovulation usually about 14 days before the next period.
- NHS (UK). Natural family planning (fertility awareness) (web page, checked Oct 2026). Used for: why calendar methods are not reliable birth control: about 24 in 100 women get pregnant in a year when instructions are not followed exactly.
- American College of Obstetricians and Gynecologists (ACOG). Fertility awareness-based methods of family planning (patient FAQ) (web page, checked Oct 2026). Used for: the birth-control warning.
- American College of Obstetricians and Gynecologists (ACOG). Evaluating infertility (patient FAQ) (web page, checked Oct 2026). Used for: when to see a doctor: after 12 months of trying, or 6 months if you are over 35.
Next steps
Questions
What is the best time to get pregnant?
The 2 days before ovulation and the day of ovulation. Sperm need to be waiting when the egg is released, so do not wait for a positive ovulation test before trying; start a few days earlier.
Can I get pregnant right after my period?
It is less likely but possible, especially with short cycles. With a 24-day cycle the fertile window can start on day 5, while you may still be bleeding.
My cycles are irregular. Can I still use it?
Yes, but treat the dates as a rough guide. Use your average cycle length, and add ovulation test strips to find your fertile days more exactly. If cycles are often under 24 or over 38 days, see a doctor.
When can I take a pregnancy test?
From the day your period is due. Home tests work best with the first urine of the morning. If it is negative and your period still has not come, test again 3 days later.
Can I use this calculator to avoid pregnancy?
No. Ovulation timing varies too much from cycle to cycle for a calendar to be used as birth control. Speak to your doctor about contraception.
Can it tell me if I will have a boy or a girl?
No. Timing sex around ovulation does not reliably change the chance of a boy or a girl, and in India finding out the sex of a baby before birth is illegal under the PCPNDT Act.
Is anything saved?
No. Everything is calculated on your phone or computer. Nothing is stored, sent to us or shared.
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Also read: stages of pregnancy