Calculating pregnancy weeks starts from the first day of your last period and is expressed in weeks and days (for example 8+3, meaning 8 weeks and 3 days). Knowing exactly where you are is the first step to scheduling visits and tests at the right time and to going through each stage of your pregnancy with peace of mind.
When do you start counting pregnancy weeks?
Weeks are counted from the first day of your last period, even though conception usually takes place about two weeks later. The reason is practical: the date of the last period is almost always known with certainty, whereas the date of conception rarely is. Doctors therefore prefer to start from a reliable figure, keeping those two weeks' difference in mind.
How to read the dating (example: 8+3)
Pregnancy is dated in weeks and days: the first number indicates the completed weeks, the second the days of the current week. So 8+3 means 8 weeks and 3 days. It is a universal language that lets any doctor or midwife immediately understand where you are.
Pregnancy weeks table month by month
Here is how the weeks are spread across the nine months. Remember that 0+0 corresponds to the first day of your last period:
- Month 1 – from 0+0 to 4+3
- Month 2 – from 4+4 to 8+5
- Month 3 – from 8+6 to 13+1
- Month 4 – from 13+2 to 17+4
- Month 5 – from 17+5 to 21+6
- Month 6 – from 22+0 to 26+2
- Month 7 – from 26+3 to 30+4
- Month 8 – from 30+5 to 35+0
- Month 9 – from 35+1 to 40+0
How to calculate your estimated due date
The estimated due date (EDD) is worked out by adding 40 weeks to the first day of your last period. A quick method is Naegele's rule: to the first day of the last period you add 7 days and subtract 3 months. The estimate is then refined by the first-trimester ultrasound, which remains the most accurate reference, especially if you have irregular cycles.
Why keep track of your pregnancy week
Each stage has its own specific check-ups and tests: from the first ultrasounds to first-trimester screenings, through to the final monitoring. Noting the current week helps you answer confidently the professionals following you and not miss important appointments. A small pregnancy diary, on paper or digital, is a simple and valuable tool.
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Frequently asked questions about calculating pregnancy
When do you start counting pregnancy weeks?
From the first day of your last period, not from conception.
What does the notation 8+3 mean?
Eight completed weeks plus three days.
How many weeks does a full-term pregnancy last?
On average 40 weeks; delivery between the 37th and 42nd week is considered physiological.
The information in this article is for general guidance and does not replace the advice of your doctor or midwife, who should always be consulted for your specific situation.
