NHS Pregnancy Calculator: Due Date and Key Dates
Your due date, how many weeks pregnant you are and your NHS appointment dates.
Your details
The day your last period started, not the day it ended.
From the first day of one period to the first day of the next. Most cycles are about 28 days.
Estimated due date
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Enter a date to see your due date
An estimate only. Only a small share of babies arrive on their due date, and most are born between 37 and 42 weeks. Your dating scan gives the most accurate due date. Appointment timings are typical for England and can differ locally. This is not medical advice.
How it is worked out
- 1Pregnancy is counted from the first day of your last period. Your due date is 40 weeks (280 days) after it, for a 28-day cycle.
- 2For a longer or shorter cycle, the due date moves by the difference from 28 days. From a conception date we add 266 days. From an IVF transfer we add 261 days for a day 5 embryo or 263 days for a day 3 embryo.
- 3Appointment and scan dates use the usual NHS timings. Maternity leave dates use the expected week of childbirth, which runs Sunday to Saturday and includes your due date.
Worth knowing
- Most babies are born between 37 and 42 weeks. The 12-week dating scan gives the most accurate due date, and your midwife will use it.
- If you work for the NHS, you qualify for NHS maternity pay with 12 months of continuous NHS service by the 11th week before your due week.
Common questions
How is my due date worked out?+
Add 280 days (40 weeks) to the first day of your last period, for a 28-day cycle. The NHS due date calculator uses the same method, and your dating scan then confirms it.
How many weeks pregnant am I?+
Count from the first day of your last period, not from conception. So at conception you are already about 2 weeks pregnant.
When is the dating scan and the 20-week scan?+
In England the dating scan is offered between 10 and 14 weeks, and the 20-week screening scan usually between 18 and 21 weeks.
When do I have to tell my employer I am pregnant?+
By the end of the 15th week before the week your baby is due, you need to tell your employer when the baby is due and when you want your maternity leave to start.
When can I get my MATB1 form?+
A midwife or doctor can give you a MATB1 certificate from 20 weeks before your due date. You give it to your employer as proof of pregnancy for maternity pay.
Sources
The rules and figures behind this calculator come from:
- NHS: Due date calculator
- NHS: Antenatal care and appointments
- NHS: 12-week scan
- NHS: 20-week scan
- NHS: Vaccinations in pregnancy
- GOV.UK: Maternity pay and leave, how to claim
- GOV.UK: Maternity leave
- NHS Terms and Conditions of Service Handbook: Section 15, leave and pay for new parents
An estimate for general information, not medical advice. Your midwife and dating scan confirm your due date. Appointment timings are typical for NHS care in England and can vary locally.
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