20-Week Scan Calculator UK
Estimate when your NHS 20-week anomaly scan may happen, based on your due date or the first day of your last period.
This page is for general pregnancy planning and date guidance only. It is not medical advice, diagnosis, or treatment. Pregnancy dates are estimates and can change after a scan or advice from your midwife, GP, or maternity team.
If you have symptoms, concerns, or questions about your pregnancy, speak to your midwife, GP, or maternity team. For urgent help, use NHS 111; call 999 in an emergency. Read how we source and review content in our editorial policy.
20-week scan window calculator
Enter either your due date or the first day of your last period to estimate the usual 18 to 21 week NHS anomaly scan window.
What is the 20-week scan?
The 20-week scan is also called the mid-pregnancy scan or anomaly scan. In England, it is usually offered between 18 and 21 weeks of pregnancy. It checks your baby's physical development and looks at several parts of the body.
What happens at the scan?
A sonographer looks carefully at your baby's development, including the brain, spine, heart, bones, face, kidneys, and abdomen. The scan may also check the position of the placenta.
Related weeks
If your scan is coming up, these week guides may be useful:
Sources and further reading
Checked for UK 20-week scan timing guidance in July 2026.
We prioritise official NHS and GOV.UK guidance, then relevant professional-body information where needed.
Source links are checked on the review date shown above. Your midwife, GP, maternity team, fertility clinic, or employer can give advice that is more specific to your circumstances.