A little help from MamaSkin
How many weeks pregnant am I?
See your weeks on any date, or find the day you’ll reach a particular pregnancy week.
Your estimate will appear here
Add your dates to see your pregnancy in weeks and days.
Your weeks, explained
Pregnancy is usually dated in completed weeks and days. This tool counts back from a due date of 40 weeks, or estimates one from your last period.
A scan or your care team may give you different dates. Their agreed dating should guide your care.
How we calculate it
Due date = first day of last period + 280 days + (usual cycle length − 28 days).
Pregnancy days on a chosen date = 280 − the number of days from that date to the due date. We divide by 7 to show completed weeks and the remaining days.
Cycle adjustment is a rough assumption about ovulation timing. It cannot establish when you ovulated or conceived. The tool supports estimates from 0 to 42 weeks and has a separate IVF calculator for embryo-transfer dating.
Sources & a note from us
We’ve used established pregnancy-dating conventions. These sources explain the approach; they haven’t reviewed or endorsed this calculator.
Sources checked 27 October 2026. General information, not a diagnosis or personal medical advice. This calculator cannot confirm pregnancy.
A worked example
Using an example due date of 11 May 2027, the result on 27 October 2026 is 12 weeks and 0 days. On 3 November, it becomes 13 weeks and 0 days.
Example dates only. Your own result uses the dates you enter.
Your questions, answered
What does “weeks and days” mean?
The result shows completed weeks plus the extra days. For example, 19 weeks and 4 days means 19 full weeks have passed, followed by another 4 days.
Why do pregnancy weeks start before conception?
Gestational age is conventionally counted from the start of the last period, rather than the day of conception. A due date represents 40 weeks in this calendar system.
Which date should I use?
Use a due date agreed with your care team when you have one. Otherwise, the last-period option gives a rough estimate for regular cycles. It uses the same calculation as our due date tool.
When will I be 20 weeks pregnant?
Choose your due date, then select “When I’ll reach a particular week”. Enter 20 completed weeks and 0 extra days. You can use the same option for another week or day, up to 42 weeks and 0 days. This finds a calendar date; it does not set a scan or care schedule.
Can I calculate my weeks for a future appointment?
Yes. Change “Calculate for” to the appointment date. The result is a calendar calculation; it does not decide when you should book a scan or receive care.
A skincare question, too?
If you’re wondering about a bottle on your shelf, our ingredient checker is a good place to start.
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