---
title: "Ovulation Calculator: Fertile Days in Hijri & Gregorian"
description: "Find your fertile window and ovulation day for the next 3 cycles, in Gregorian and Hijri dates. Free and private: nothing leaves your browser."
url: https://periodcalc.app/ovulation-calculator/
lang: en
---
# Ovulation calculator

Your fertile days and ovulation for the next three cycles — in Gregorian and Hijri.

- Gregorian + Hijri (Umm al-Qura)
- Nothing leaves your browser
- Free, no sign-up

Ovulation usually happens about 14 days before your next period starts — on day 15 of a 28-day cycle (often quoted as day 14), counting the first day of your period as day 1. You can get pregnant from 5 days before ovulation to 1 day after it, according to [ACOG](https://www.acog.org/womens-health/faqs/fertility-awareness-based-methods-of-family-planning).

By [Hossam Hamouda](https://periodcalc.app/about/), developer of Period Calc · Last updated: 23 October 2026

## How ovulation is estimated

Ovulation is the day an ovary releases an egg. It usually happens about 14 days before your next period starts ([NHS](https://www.nhs.uk/pregnancy/trying-for-a-baby/trying-to-get-pregnant/)) — in most women, 10 to 16 days before it ([NHS](https://www.nhs.uk/conditions/periods/fertility-in-the-menstrual-cycle/)). So the calculator first predicts your next period from the first day of your last period and your cycle length, then counts back 14 days.

An egg lives for about a day, but sperm can survive in the body for up to five days ([ACOG](https://www.acog.org/womens-health/faqs/fertility-awareness-based-methods-of-family-planning)). That is why the fertile window is longer than one day. The calculator marks seven days — the five days before ovulation, ovulation day and the day after — the same window the Period Calc app uses, and highlights the two days before ovulation and ovulation day as your most fertile days. On very short cycles the window can begin right after a period ends (see the [table](https://periodcalc.app/ovulation-calculator/#reference-table)).

## The formula

Next period = first day of last period + cycle length

Ovulation ≈ next period − 14 days

Fertile window = ovulation − 5 days to ovulation + 1 day

## A worked example

Your last period started on **10 June 2026** and your cycles are **28 days** long.

- **Next period**: 8 July 2026 (10 June + 28 days)
- **Ovulation**: around 24 June 2026 (8 July − 14 days)
- **Fertile window**: 19–25 June 2026
- **In the Hijri calendar**: the fertile window runs from 4 Muharram 1448 to 10 Muharram 1448, with ovulation around 9 Muharram 1448

With a 32-day cycle, the same start date moves ovulation to around 28 June 2026: a longer cycle means a later ovulation, and a shorter cycle an earlier one.

## Ovulation day for every cycle length

On cycles of 21 to 23 days the window starts on day 6: like the calculator, the table assumes a 5-day period and never counts period days as fertile.

Estimated ovulation day and fertile window for each cycle length, in days of the cycle (day 1 = the first day of your period)

| Cycle length | Ovulation day | Fertile window |
|---|---|---|
| 21 | 8 | 6–9 |
| 22 | 9 | 6–10 |
| 23 | 10 | 6–11 |
| 24 | 11 | 6–12 |
| 25 | 12 | 7–13 |
| 26 | 13 | 8–14 |
| 27 | 14 | 9–15 |
| 28 (average) | 15 | 10–16 |
| 29 | 16 | 11–17 |
| 30 | 17 | 12–18 |
| 31 | 18 | 13–19 |
| 32 | 19 | 14–20 |
| 33 | 20 | 15–21 |

| Cycle length | Ovulation day | Fertile window |
|---|---|---|
| 34 | 21 | 16–22 |
| 35 | 22 | 17–23 |
| 36 | 23 | 18–24 |
| 37 | 24 | 19–25 |
| 38 | 25 | 20–26 |
| 39 | 26 | 21–27 |
| 40 | 27 | 22–28 |
| 41 | 28 | 23–29 |
| 42 | 29 | 24–30 |
| 43 | 30 | 25–31 |
| 44 | 31 | 26–32 |
| 45 | 32 | 27–33 |

## Signs that ovulation is near

Your body often gives clues. In the days before ovulation, cervical mucus becomes thin, stretchy and slippery, a bit like raw egg white. Around ovulation, your resting body temperature rises slightly and stays up until your next period. Ovulation tests from a pharmacy detect the rise in luteinising hormone (LH) that comes a day or two before ovulation ([ACOG](https://www.acog.org/womens-health/faqs/evaluating-infertility)).

## If your cycles are irregular

When your cycle length changes from month to month, ovulation moves too, and an estimate based on dates becomes less reliable. Use your average cycle length, and combine the calculator with the body signs above or with ovulation tests for a clearer picture.

## When to see a doctor

See a doctor if you have been trying to get pregnant for a year without success — or for six months if you are over 35 ([ACOG](https://www.acog.org/womens-health/faqs/evaluating-infertility)). If you are over 40, talk to a doctor now rather than waiting.

Want to see your next periods as well? The [period calculator](https://periodcalc.app/period-calculator/) shows six cycles and a calendar. If you are already pregnant, the [due date calculator](https://periodcalc.app/due-date-calculator/) estimates your due date, and the [Period Calc FAQ](https://periodcalc.app/faq/) answers questions about the app.

This calculator gives estimates, not medical advice. It cannot tell you which days are safe, and it is not a method of contraception.

## Questions about ovulation

### When am I most likely to get pregnant?

In the 2 to 3 days before your body temperature rises at ovulation, according to [ACOG](https://www.acog.org/womens-health/faqs/fertility-awareness-based-methods-of-family-planning); the [NHS](https://www.nhs.uk/pregnancy/trying-for-a-baby/trying-to-get-pregnant/) says you are more likely to get pregnant around the time you ovulate. The calculator highlights the two days before ovulation and ovulation day as your most fertile days. Having sex every two to three days throughout your cycle also covers your fertile window without needing to know the exact day.

### Can ovulation happen on a different day than predicted?

Yes. Ovulation is hard to pin down: in most women it happens 10 to 16 days before the next period, and it can move from one cycle to the next. Treat the result as a window, not an exact day.

### Can I get pregnant during my period?

It is unlikely, but it can happen with short cycles: your fertile window can begin soon after your period ends, and sperm can live for several days.

### Can the Period Calc app do this for me?

Yes. Choose “Trying to conceive” to see your fertile window, your estimated ovulation day and when to take a pregnancy test. Premium adds your best days, day by day, today’s chance of pregnancy and reminders before your fertile days.

### Is what I type private?

Yes. The calculation runs in your browser, and nothing you enter is sent to us or anyone else.

## How this page was made

Hossam Hamouda, the developer of Period Calc, wrote this page from the guidance of the health organisations listed under [Sources](https://periodcalc.app/ovulation-calculator/#sources). They have not reviewed it, and neither has a doctor. The calculator runs the [formula above](https://periodcalc.app/ovulation-calculator/#formula) in your browser, with the same rules as the Period Calc app. It works from averages, so it cannot know how your own body differs from them, and it cannot diagnose anything: if something worries you, see [when to see a doctor](https://periodcalc.app/ovulation-calculator/#see-a-doctor).

## Sources

1. [Periods and fertility in the menstrual cycle](https://www.nhs.uk/conditions/periods/fertility-in-the-menstrual-cycle/) (NHS)
2. [Trying to get pregnant](https://www.nhs.uk/pregnancy/trying-for-a-baby/trying-to-get-pregnant/) (NHS)
3. [Fertility Awareness-Based Methods of Family Planning](https://www.acog.org/womens-health/faqs/fertility-awareness-based-methods-of-family-planning) (ACOG)
4. [Evaluating Infertility](https://www.acog.org/womens-health/faqs/evaluating-infertility) (ACOG)
5. [Infertility](https://www.who.int/news-room/fact-sheets/detail/infertility) (WHO)

## Get reminders before your next period

**Period Calc** for iPhone learns from your own cycles and reminds you two days before your period — discreetly, with no details unless you turn them on.

- The Hijri date on every calendar day
- Your fasting days, every month
- A PIN and Face ID lock, and no account

[Download on the App Store](https://apps.apple.com/app/id6814298894)

## Free calculators

- [Period calculator](https://periodcalc.app/period-calculator/): Your next six periods, fertile days and ovulation, in Gregorian and Hijri dates.
- [Due date calculator](https://periodcalc.app/due-date-calculator/): Your due date, how many weeks pregnant you are and your trimester.
- [Pregnancy week calculator](https://periodcalc.app/pregnancy-week-calculator/): How many weeks and days pregnant you are, your trimester and due date, from your last period or your due date.
- [Conception date calculator](https://periodcalc.app/conception-date-calculator/): Count back from your due date to the days you most likely conceived: an estimate, not an exact day.
- [Pregnancy test date calculator](https://periodcalc.app/pregnancy-test-date/): Shows the day your next period is due. The NHS says most tests can be done from the first day of a missed period.

## Related guides

To check your estimate against what your body shows, read the guide to the [signs of ovulation](https://periodcalc.app/signs-of-ovulation/) and how far to trust each one.

Already pregnant and wondering when you conceived? The [conception date calculator](https://periodcalc.app/conception-date-calculator/) counts back from your due date.

If your cycles are often irregular, read about [irregular periods](https://periodcalc.app/irregular-periods/) too.

- [Late period](https://periodcalc.app/late-period/): Pregnancy and stress are common reasons for a late period, and most home tests work from the first day you miss it.
- [How long a period lasts](https://periodcalc.app/how-long-does-a-period-last/): A period usually lasts 2 to 7 days and a cycle 21 to 35 days.
- [Signs of ovulation](https://periodcalc.app/signs-of-ovulation/): Mucus, temperature, tests and pain can show ovulation, but a temperature rise only confirms it afterwards.
- [Irregular periods](https://periodcalc.app/irregular-periods/): The NHS calls periods irregular when the gap is under 21 or over 35 days, and says they are not usually a sign of a problem.

Predictions are estimates, not medical advice or a diagnosis, and not a method of contraception.

The prayer & purity guide gives the general rules of the four schools. It is not a fatwa — for your own case, ask someone whose knowledge you trust.

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