---
title: "Guides and Calculators for Periods, Ovulation and Pregnancy"
description: "Free calculators and clear guides on periods, ovulation and pregnancy. Health numbers link to the NHS, ACOG or WHO page they come from."
url: https://periodcalc.app/guides/
lang: en
---
# Guides and calculators

Every free calculator and guide on this site. Each page starts with a short answer to one question.

## Calculators

- [Period calculator](https://periodcalc.app/period-calculator/): Your next six periods, fertile days and ovulation, in Gregorian and Hijri dates.
- [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.

## Guides

- [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.

## What you will find here

Period Calc is a period tracker and planner for iPhone, made for Muslim women. The calculators on this site work out dates such as your next period, fertile days, due date and pregnancy week from your own dates, in the Gregorian and Hijri calendars. Nothing you type leaves your browser.

The guides are plain-English answers to the questions behind those dates. Start with a calculator for your own dates, then read a guide for what is usual and when to ask a doctor.

## How the guides are made

Each guide starts with a short answer to one question, then explains. The health guides link the health numbers to the NHS (the UK’s National Health Service), ACOG (the American College of Obstetricians and Gynecologists) or the WHO (the World Health Organization) page they come from. They also say when to see a doctor.

[Hossam Hamouda](https://periodcalc.app/about/), the developer of Period Calc, writes the guides. Those organisations have not reviewed the health guides, and neither has a doctor. The guides give general information, not medical advice, and they are not a method of contraception.

Looking for answers about the app instead? See the [FAQ](https://periodcalc.app/faq/) or [Support](https://periodcalc.app/support/).

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.