---
title: "Period Calculator with Hijri Dates — Free & Private"
description: "Free period calculator: see your next 6 periods, fertile days and ovulation in Gregorian and Hijri dates. It runs in your browser — nothing is sent."
url: https://periodcalc.app/period-calculator/
lang: en
---
# Period calculator

Your next six periods, fertile days and ovulation — every date in Gregorian and Hijri.

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

Your next period is due one cycle length after the first day of your last period: 28 days later if your cycle is 28 days long. Most cycles last 21 to 35 days and most periods 2 to 7 days, according to the [NHS](https://www.nhs.uk/conditions/periods/fertility-in-the-menstrual-cycle/).

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

## How the period calculator works

Your menstrual cycle starts on the first day of your period and ends the day before your next period begins. The calculator takes the day your last period started and adds your usual cycle length, again and again, to estimate when your next periods will start. Each one then lasts your usual period length.

Ovulation usually happens about 14 days (in most women 10 to 16 days) before the next period starts ([NHS](https://www.nhs.uk/conditions/periods/fertility-in-the-menstrual-cycle/)), so the calculator counts back 14 days from each predicted start. You can get pregnant from 5 days before ovulation to 1 day after it, and the most fertile days are the 2 to 3 days before your body temperature rises at ovulation ([ACOG](https://www.acog.org/womens-health/faqs/fertility-awareness-based-methods-of-family-planning)). The calculator marks that whole fertile window and the ovulation day; the [ovulation calculator](https://periodcalc.app/ovulation-calculator/) also highlights the two days before ovulation and ovulation day as your most fertile days, for the next three cycles. Every date is also shown in the Hijri calendar (Umm al-Qura), so you can see where your period may fall in the Hijri month.

## 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

Say your last period started on **3 September 2026**, your cycles are usually **30 days** long and your period lasts **6 days**.

- **Next period**: 3–8 October 2026 (3 September + 30 days)
- **Ovulation**: around 19 September 2026 (3 October − 14 days)
- **Fertile window**: 14–20 September 2026
- **The period after**: 2–7 November 2026 (3 October + 30 days)
- **In the Hijri calendar**: your period started on 21 Rabi I 1448, the next one is due on 22 Rabi II 1448 and ovulation is around 8 Rabi II 1448

Hijri months last 29 or 30 days, so with a 30-day cycle each period starts on the same day of the Hijri month as the one before, or up to a day later. The calculator shows every date in both calendars, so you can plan by either.

## If your cycles are irregular

Most cycles last between 21 and 35 days ([NHS](https://www.nhs.uk/conditions/periods/fertility-in-the-menstrual-cycle/)), and it is normal for yours to change by a few days from month to month. If your cycle length varies, enter your average: add up the lengths of your last few cycles and divide by how many there were. The further ahead a date is, the less precise it gets, so treat the later periods as a rough guide. If your next period would already be more than 90 days late, the calculator asks for a more recent date.

Stress, losing or gaining a lot of weight, exercising a lot, hormonal contraception and conditions such as polycystic ovary syndrome (PCOS) or thyroid problems can all make cycles irregular. In those months, an estimate based on dates alone can be several days out. The **Period Calc** app learns from your own cycles: it averages your last six logged cycles and tells you when they vary a lot.

## When to see a doctor

Talk to a doctor or nurse if:

- your periods stop for three months or more and you are not pregnant ([ACOG](https://www.acog.org/womens-health/faqs/abnormal-uterine-bleeding));
- the time between your periods is often shorter than 21 days or longer than 35 days ([NHS](https://www.nhs.uk/symptoms/irregular-periods/));
- your period lasts longer than 7 days or is very heavy ([NHS](https://www.nhs.uk/conditions/heavy-periods/));
- your cycle length often changes by more than 7 to 9 days from one month to the next ([ACOG](https://www.acog.org/womens-health/faqs/abnormal-uterine-bleeding));
- you bleed between periods or after sex, or have severe pain during your periods;
- your periods are irregular and you are struggling to get pregnant.

If your period is late and you might be pregnant, a pregnancy test can tell you. The [due date calculator](https://periodcalc.app/due-date-calculator/) then works out your due date and how many weeks along you are. More answers about the app, privacy and the Hijri calendar are in the [Period Calc FAQ](https://periodcalc.app/faq/).

This calculator gives estimates based on averages. It is not medical advice or a diagnosis, and it is not a method of contraception.

## Questions about the period calculator

### When will my next period come?

Add your usual cycle length to the first day of your last period. If your last period started on 3 May and your cycle is 28 days long, your next period is due around 31 May. The calculator above does this for your next six cycles, with every date in the Hijri calendar too.

### How accurate is a period calculator?

It is as accurate as your cycles are regular. If your cycle is about the same length every month, the predicted dates are a good guide; if it varies, expect your period to start several days earlier or later. The Period Calc app learns from your own dates.

### What cycle length should I enter?

Count the days from the first day of one period to the day before the next one starts. If you are not sure, start with 28 days — the average length — and adjust once you have followed a few cycles.

### Can I use it to avoid pregnancy?

No. This calculator only gives estimates: ovulation can move from cycle to cycle and sperm can live for several days, so a calculator based on dates cannot tell you which days are safe. It is not a method of contraception.

### Why are the dates also shown in the Hijri calendar?

Many Muslim women plan fasting, prayer and travel by the Hijri month. The calculator uses the Umm al-Qura calendar, so the Hijri date where you live may differ by a day.

### Is what I type saved or sent anywhere?

No. The calculation runs in your browser. Nothing you enter is sent to us or anyone else, and this website uses no cookies or analytics.

## 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/period-calculator/#sources). They have not reviewed it, and neither has a doctor. The calculator runs the [formula above](https://periodcalc.app/period-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/period-calculator/#see-a-doctor).

## Sources

1. [Irregular periods](https://www.nhs.uk/symptoms/irregular-periods/) (NHS)
2. [Heavy periods](https://www.nhs.uk/conditions/heavy-periods/) (NHS)
3. [Periods and fertility in the menstrual cycle](https://www.nhs.uk/conditions/periods/fertility-in-the-menstrual-cycle/) (NHS)
4. [Abnormal Uterine Bleeding](https://www.acog.org/womens-health/faqs/abnormal-uterine-bleeding) (ACOG)
5. [Fertility Awareness-Based Methods of Family Planning](https://www.acog.org/womens-health/faqs/fertility-awareness-based-methods-of-family-planning) (ACOG)

## 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

- [Ovulation calculator](https://periodcalc.app/ovulation-calculator/): Your fertile window and ovulation day for the next three cycles.
- [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

If your cycles are often very short, very long or change a lot from month to month, read about [irregular periods](https://periodcalc.app/irregular-periods/): what counts, the causes and what to tell your doctor.

Is your period late? The [pregnancy test date calculator](https://periodcalc.app/pregnancy-test-date/) shows the day your next period is due, and [why a period is late](https://periodcalc.app/late-period/) explains the common reasons.

Wondering what is a normal period or cycle length? Read [how long a period lasts](https://periodcalc.app/how-long-does-a-period-last/).

- [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.

This website uses no cookies and no analytics. The calculators run in your browser, and nothing you type is sent anywhere.