When you only roughly know your last period
Lots of people don’t track their periods, have irregular cycles, or simply can’t remember the exact date — especially if the pregnancy was a surprise. Standard calculators need an exact date, so this estimator works from what you do remember: the month your last period started and, if you can, whether it was early, in the middle or late in that month.
It then shows a range of possible due dates and a range for how far along you are today, plus a best guess in the middle. A range is the honest answer when the starting date is uncertain.
Jog your memory
A few prompts that help many people narrow down the date:
- Check your phone: period-tracking apps, calendar entries, or photos and messages from around that time.
- Think about events — a birthday, holiday, trip or exam — and whether your period was before or after it.
- Check bank statements for period products, pain relief or a pharmacy visit.
- Count back from your first positive test: tests usually turn positive about 4 weeks after the period started. Our Estimate Pregnancy Due Date tool does this for you.
Narrowing it down with a scan
When the last period date is uncertain, an early ultrasound is the best way to date the pregnancy. A scan between about 8 and 14 weeks measures the embryo or fetus (the crown–rump length) and estimates gestational age to within about a week. Once you have a scan result, use the Ultrasound Due Date Calculator for a precise date.
What the range means for you
Until you have a scan, use the earlier end of the range for anything time-sensitive — such as booking your first appointment, starting folic acid if you haven’t already, or checking which tests are offered at your stage. Contact a doctor or midwife as soon as you know you are pregnant; they can arrange a dating scan if needed.