Pregnancy Due Date Calculator
Estimate your due date from your last period, and see how far along you are with the key dates ahead.
How your due date is worked out
First day of your last period + 40 weeks, nudged for your cycle length.
- 1
Start at your period
31 July 2026
counts as day 0 - 2
Add 40 weeks
+ 280 days
= 7 May 2027 - 3
Adjust for cycle
28 − 28 = 0 days
→ Fri 7 May 2027 - 4
How far along
70 days ÷ 7
= 10w 0d
First trimester
Read more: Naegele's rule, a worked example and dating scans
Pregnancy is usually counted from the first day of your last menstrual period, about two weeks before conception. A typical pregnancy lasts 40 weeks (280 days) from that day. This is Naegele's rule.
due date = first day of last period + 280 days (+ cycle length − 28)
If your cycle is longer or shorter than 28 days, ovulation usually happens later or earlier, so the due date moves by the same number of days.
Worked example
If your last period started on 1 January 2026 and your cycle is 28 days, your estimated due date is 8 October 2026. On 1 April 2026 you'd be 12 weeks and 6 days pregnant.
Your dating scan
An early ultrasound scan, usually between 8 and 14 weeks, measures the baby and gives the most accurate due date, especially if your cycles are irregular or you're unsure of your dates. Your midwife or doctor will use that date from then on.
For information only. Please speak to your doctor or midwife about your pregnancy and care.