What this tool does

This calculator works out when your baby is likely to arrive, based on the first day of your last period. It also tells you how many weeks and days pregnant you are today, and gives a short summary of what your baby is doing at this stage, from tiny cell clusters in the early weeks through to a fully formed baby getting ready to be born.

Who it is for

If you have just seen a positive test and want a rough idea of when the baby is due, this is a quick way to find out before your first midwife appointment. It is also useful if you are further along and want a simple reminder of what is happening week by week, or if you are trying to work out how many weeks you were at a scan or appointment.

The result is an estimate. Your midwife or sonographer will confirm a more accurate date at your dating scan, usually between 8 and 14 weeks. Only around one in twenty babies actually arrives on the estimated due date, so treat it as a guide rather than a fixed appointment.

How it works

Enter the first day of your last menstrual period and, if you know it, your average cycle length. The tool adds 280 days, adjusting for cycles that are shorter or longer than 28 days, and shows your estimated due date along with your current week of pregnancy and a short note on your baby's development. You get the information straight away on the page. Nothing you type is saved or shared, and you do not need to sign up or give an email address.

If you are not sure of the date your last period started, it is still worth putting in your best guess. Your midwife can adjust things later once you have had a scan. If you have any worries about your pregnancy, or you are bleeding or in pain, contact your GP, midwife or NHS 111 rather than relying on a calculator.