Pregnancy Calculator
Track your week, trimester and countdown to due date
Give the calculator either the first day of your last period or a known conception date, and it works out how many weeks and days along you are, which trimester you're in, and your estimated due date. It also flags the milestones ahead, so you can see at a glance what each stage of the coming weeks tends to bring.
Enter Your Details
Your Pregnancy
Progress & Stats
Trimester Guide
Why your due date is a window, not a deadline
An estimated due date is worked out as 40 weeks from the first day of your last period, which assumes a textbook 28-day cycle and ovulation around day 14. Real cycles vary, so the date is a best estimate rather than a fixed appointment. Only about one baby in twenty actually arrives on the predicted day; the large majority turn up in the fortnight either side, and anything from 37 to 42 weeks counts as full term.
If you have had a dating scan, the date it gives is usually more accurate than one based on your last period, because it measures the baby directly. This page is for interest and planning, not medical advice — your midwife or doctor remains the person to trust.
❓ Frequently Asked Questions
How is gestational age calculated? ▼
Gestational age is measured from the first day of your last menstrual period (LMP), not from conception. Enter your LMP date and the calculator adds 280 days (40 weeks) to give your estimated due date, then works backwards to show how far along you are today.
What is the difference between gestational age and fetal age? ▼
Gestational age counts from your LMP and is the standard used by doctors and midwives. Fetal age (or embryonic age) counts from conception, which is typically about 2 weeks less than gestational age.
How accurate is the due date calculation? ▼
The EDD is an estimate based on a standard 28-day cycle. Only about 5% of babies are born on their exact due date. Your midwife or doctor may adjust the EDD after an ultrasound scan for greater accuracy.
What trimester am I in? ▼
The first trimester runs from week 1 to week 12, the second trimester from week 13 to week 26, and the third trimester from week 27 to week 40 (or birth). The calculator shows your current trimester automatically.
Can I calculate based on conception date instead of LMP? ▼
Yes — select "Conception date" from the input mode toggle. The calculator adds 266 days (38 weeks) from conception to give your estimated due date.
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