What is an ovulation calculator?
An ovulation calculator predicts the day your ovary is likely to release an egg and the handful of days each month when you can get pregnant, called the fertile window. Enter the first day of your last period and your average cycle length, and this free online ovulation calculator shows your next ovulation date, your most fertile days, the date to take a pregnancy test and a table of fertile windows for the next three cycles. It is a simple way to plan intercourse when you are trying to conceive.
What is ovulation?
Ovulation is the release of a mature egg from the ovary into the fallopian tube, triggered by a surge of luteinising hormone (LH). The egg survives for only 12–24 hours, but sperm can live in the female reproductive tract for up to 5 days. That is why the fertile period is about six days long: the five days before ovulation and the ovulation day itself. The ovulation phase sits in the middle of the menstrual cycle, between the follicular phase (period to ovulation) and the luteal phase (ovulation to next period).
How to calculate ovulation day
The luteal phase is fairly constant at about 14 days in most women, while the first half of the cycle varies. So ovulation is counted backwards from the next period:
Ovulation day = first day of last period + (cycle length − 14)
Fertile window = ovulation day − 5 days to ovulation day + 1 day
- Cycle length = days from the first day of one period to the first day of the next
- 14 = average luteal phase length (you can change it if you know yours)
How to calculate ovulation day for a 30 days cycle
If your last period began on 1 September and your cycle is 30 days, ovulation is on day 30 − 14 = 16, which is 16 September. Your fertile window runs from 11 to 17 September, and your next period is due on 1 October. For a 28-day cycle, ovulation falls on day 14; for a 35-day cycle, on day 21.
| Cycle length | Ovulation day | Fertile days (cycle days) |
|---|---|---|
| 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 |
How to use this ovulation calculator for pregnancy
- Enter the first day of your last period – the first day of full bleeding, not spotting.
- Enter your average cycle length over the last 3 months. If it varies, see the section on irregular periods below.
- Leave the luteal phase at 14 days unless you have tracked it.
To get pregnant, have intercourse every 1–2 days during the fertile window, especially the two days before ovulation and the ovulation day itself – these are the days with the highest chance of conception.
Ovulation calculator for irregular periods
If your cycle length changes from month to month, a calendar calculator is less reliable. Work out your shortest and longest cycles over the last few months. Your earliest fertile day is roughly shortest cycle − 18, and your latest is longest cycle − 11. For cycles between 26 and 34 days, that means days 8 to 23. Combining the calculator with ovulation test kits (LH strips), cervical mucus changes and basal body temperature gives a much clearer picture. Conditions such as PCOS commonly cause irregular ovulation; a gynaecologist may suggest tests or treatment such as letrozole.
Signs and symptoms of ovulation
- Clear, stretchy, egg-white cervical mucus.
- A small rise (0.2–0.5 °C) in basal body temperature after ovulation.
- Mild one-sided pelvic pain (mittelschmerz).
- Breast tenderness and a higher sex drive.
- A positive LH ovulation test 24–36 hours before ovulation.
Can an ovulation calculator predict a boy or girl?
Many people search for an ovulation calculator for a baby boy or girl. Timing methods such as the Shettles method claim that sex close to ovulation favours a boy and sex a few days before favours a girl, but large studies have not found timing to change the baby's sex meaningfully. The chance stays close to 50:50.
Does an ovulation calculator work?
For women with regular cycles it gives a good estimate, but ovulation can shift by a few days because of stress, illness, travel or breastfeeding. Use it as a guide, not a guarantee, and never as your only method of birth control. After ovulation, use the pregnancy due date calculator to see your due date if you conceive, and the period calculator to plan the months ahead.
Cycle length, calendar, due date and more: what to enter
Ovulation calculator online free
This ovulation calculator online free version needs no app or login, in India or anywhere else. Update the date each month and it doubles as an online ovulation tracker.
Ovulation calculator for 30 days cycle
Enter 30 days as your cycle length. That answers how to calculate ovulation period for 30 days cycle: ovulation around day 16.
Using your last 3 months of periods
Average your last three cycles (the last 3 months of periods) and enter that average as the cycle length in the ovulation calculator for the best forecast. Two periods work too, but three or more is better.
Calendar: monthly and yearly
The table shows three cycles, so you can use the ovulation calculator as a monthly calendar. For a view of the whole year, update your period date in the ovulation calculator each month and check the next three cycles.
Pregnancy test date and next period
The result also predicts your next period. Take a pregnancy test on the day it is due.
Ovulation calculator with due date
If you conceive this cycle, the result shows your due date too, so you can plan ahead.
Irregular or varying cycle length
If your cycle length varies, run the calculator twice – once with your shortest cycle and once with your longest – and treat all days from the first window to the second as fertile. This is how to calculate ovulation date in irregular periods, and why irregular periods call for extra signs like LH kits.
Ovulation calculator with letrozole
Letrozole changes the timing: when it is taken on days 3–7, ovulation usually happens around days 12–16. Your doctor may track it with follicle scans rather than a calendar.
Ovulation calculator in Hindi, Tamil and Marathi
Ovulation is "andotsarg" in Hindi. The maths is the same in any language: enter dates here and read the results.
Boy or girl?
As explained above, timing sex cannot reliably choose a baby boy or a girl.
Ovulation calculator: how to get pregnant
The plan is simple: have sex every 1–2 days across the fertile window shown. The calculator helps you calculate ovulation date and answers "when am I ovulating?". For how to calculate ovulation period after menstruation, subtract your period length from the ovulation day.
What is the ovulation period in woman? It is the fertile window of about six days each cycle. What is ovulation day? The single day the egg is released. That is how does ovulation calculator work: it counts back 14 days from the next period, which is how to calculate ovulation for any regular cycle.
The cycle-length table above works as a quick ovulation calculator chart: find your cycle, read the days column and add them to your period start to get the date. That is how can i calculate ovulation day without any app.
How can we calculate ovulation? Ovulation calculator formula and example
Ovulation usually happens about 14 days before the next period starts, so subtract 14 from your cycle length to find the ovulation day. The fertile window is the 5 days before ovulation plus the day itself.
July ovulation calculator example
Your last period started on 3 July and your cycle is 28 days. Ovulation day = 28 − 14 = day 14, which is 16 July. The fertile window runs from 11 July to 16 July, and your next period is due on 31 July. With a 32-day cycle, ovulation moves to day 18 (20 July) and the window to 15–20 July.
Ovulation calculator: how many days does ovulation last?
The egg lives for only 12–24 hours after it is released, but sperm can survive up to 5 days, which is why the fertile window is about 6 days long.
Ovulation calculator with percentage chance by day
Research on couples trying to conceive found that the chance of pregnancy from sex on a single day is highest in the 2 days before ovulation and on ovulation day, at roughly 20–30% per cycle for healthy couples, falls to under 10% five days before, and is close to zero the day after. That is why the ovulation calculator highlights the whole window, not just one day.
Ovulation calculator Indian users: same method, local support
The ovulation calculator works the same for Indian women as for anyone else, because it depends only on cycle length. Irregular cycles are common in India, often linked to PCOS; if your cycle varies by more than 7–9 days, the predicted window is less reliable, and ovulation test kits or a doctor's follicle scan give a better answer.
Ovulation calculator symptoms check
Use the calculator's date together with body signs: clear, stretchy cervical mucus, a small rise in basal body temperature (about 0.2–0.5 °C) after ovulation, mild one-sided pelvic pain and a positive LH test. If these line up with the ovulation calculator's predicted window, your estimate is likely right.
Ovulation calculator for boy or twins: what is possible
No ovulation calculator can choose a boy, a girl or twins. Timing methods for a boy have not been shown to work in good studies. Non-identical twins happen when two eggs are released in one cycle, which is more likely with age over 30, a family history of twins and fertility treatment, but it cannot be planned through timing.
Frequently asked questions
How do I calculate my ovulation days?
Subtract 14 from your cycle length to find the ovulation day, counting the first day of your period as day 1. Your fertile days are the 5 days before ovulation plus the ovulation day.
How many fertile days are there in a month?
About six: the five days before ovulation and the day of ovulation. The two days before ovulation are the most fertile.
How do I calculate ovulation for a 30-day cycle?
Ovulation is around day 16 (30 − 14), and the fertile window is roughly days 11 to 17.
Does the ovulation calculator work for irregular periods?
It is less accurate. Use your shortest and longest cycles to find a wider window, and confirm with LH ovulation kits or cervical mucus changes.
When should I take a pregnancy test?
Take a home pregnancy test from the day your period is due. The calculator shows this date.
Can I get pregnant outside my fertile window?
It is unlikely but possible, because ovulation can come earlier or later than predicted. Do not rely on the calendar method for contraception.
How long after my period do I ovulate?
In a 28-day cycle with a 5-day period, ovulation is about 9 days after the period ends. In longer cycles it comes later.
How many days does ovulation last?
The egg survives 12–24 hours after release, but because sperm can live up to 5 days, the fertile window is about 6 days.
Can I plan twins with an ovulation calculator?
No. Twins cannot be planned through timing. Non-identical twins are more likely with age over 30, a family history of twins or fertility treatment.
Last updated 2026-09-18