---
title: "How many weeks pregnant am I? Work it out | PERIOD."
description: "Work out for free how many weeks and days pregnant you are, which trimester you are in and how many days are left until your due date."
url: https://myperiod.app/en/tools/pregnancy-week-calculator
lang: en
publisher: PERIOD. B.V., Amsterdam
---

[Free tool](https://myperiod.app/en/tools)

# How many weeks pregnant am I?

Pregnancy is counted from the first day of your last period, not from conception. Count the days since that date and divide by 7. If you know your due date, we count back from 40 weeks. Enter either one below.

Calculate from

First day of your last period

Average cycle length days

Enter a date to calculate.

Everything is calculated on your own device. We store nothing and send nothing anywhere.

This is an estimate, not medical advice and not contraception. If in doubt, ask your GP or midwife.

## How we calculate

A pregnancy lasts 40 weeks, counted from the first day of your last period. If you enter that date, we take your cycle length into account. If you enter your due date, we count back from 40 weeks.

## The trimesters

The first trimester runs to 14 weeks, the second to 28 weeks and the third until birth.

## Follow it week by week

In PERIOD. baby you follow your pregnancy week by week, with how big your baby is and what is happening.

## Want to know every month, without the maths?

PERIOD. learns from your own cycles and keeps your predictions up to date. Free, no ads, and we never sell your data.

4.8 ★★★★★ on the App Store

100,000+ women

## Frequently asked questions

### When do pregnancy weeks start?

From the first day of your last period. That is why you are officially already about 2 weeks pregnant at conception.

### How many weeks does a pregnancy last?

On average 40 weeks from the first day of your last period. Between 37 and 42 weeks counts as on time.

### When does the second trimester start?

At around 14 weeks. The third trimester starts at around 28 weeks.

### My scan says a different week, which is right?

Follow the scan: it is more accurate than counting from your last period.

## Read more

- [Early signs of pregnancy](https://myperiod.app/en/blog/eerste-tekenen-zwangerschap)

## Other free tools

- [Period calculator](https://myperiod.app/en/tools/period-calculator)
- [Ovulation calculator](https://myperiod.app/en/tools/ovulation-calculator)
- [Due date calculator](https://myperiod.app/en/tools/due-date-calculator)

Sources: NHS, Periods and fertility in the menstrual cycle; NHS, Pregnancy due date; ACOG, Methods for estimating the due date.