# Due date calculator - calculate your baby's due date

You just found out that you are pregnant? - Congratulations! Of course you now want to calculate your baby's due date instantly.
Our baby due date calculator helps you with this!

**Warning**Please understand that we cannot guarantee for the calculated values to be 100% accurate. Every pregnancy is different. Depending on the development of your pregnancy it may be that your gynaecologist or midwife pre-dates or back-dates the calculated due date.

## How our due date calculator works

Author: Janina Wolf

Our **due date calculator** works according to Naegele's law (German scientist),
which basically states that your pregnancy lasts 40 weeks (280 days) starting
from the first day of your last period. So you will need this date in order to use our due date calculator.

To have our calculator estimate your baby's due date even more precisely, you may also enter your average cycle length (measured over the last 3-5 cycles). Your cycle length influences your ovulation and with it your conception date and due date.

## Due date calculator - what to expect?

Please note that the calculated due date will only be a best guess - only 5% of all babies will be born exactly at that date. More than 70% of the babies are born between 3 weeks before or 2 weeks after the due date, 25% within a range of one week before or after. So, if you don't know your average cycle length or the first day of your last period exactly - that won't really matter.

## How to calculate your due date offline

With the following formula, you may calculate your baby's due date very easily offline (for an average cycle length of 28 days).

### Formula

first day of your last period

-3 month

+1 year

+7 days

-------------

= **due date**

### Example calculation

first day of your last period: 08/10/2013

-3 month (= 05/10/2013)

+1 year (= 05/10/2014)

+7 days (= 05/17/2014)

-------------

= **due date: 05/17/2014**

So in our example calculation, the due date for your baby would be 05/17/2014.

### How the average cycle length affects your due date

As a rule of thumb you may add (or substract) the difference in days of your average cycle length to (from) the calculated due date. So for instance if your average cycle length was 32 days, you would add 4 days to the result. In our calculation example above that would then be 05/21/2014.

**Author: Janina Wolf**