Baby & family
Pregnancy Week Calculator
See how many weeks pregnant you are today, which trimester you're in, roughly how big your baby is this week and how many days are left until your due date.
Your result
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How to use this calculator
Enter the first day of your last menstrual period (LMP), or your due date if your doctor or midwife has already given you one. The calculator counts the weeks and days since your LMP, which is how pregnancy is measured, and shows your trimester and a fun size comparison for the week.
How pregnancy weeks are counted
Due date = Last period + 280 days (40 weeks) Counting starts from your last period, about two weeks before conception, so at "4 weeks pregnant" the embryo is about 2 weeks old. If you entered a due date, your LMP is taken as the due date minus 280 days.
Worked example
- 73 ÷ 7 = 10 weeks and 3 days, written 10w 3d
- You're in the first trimester (weeks 0–13)
- Estimated due date: January 1 + 280 days = October 8, 2026
Trimesters at a glance
- First trimester (weeks 1–13): early development of the baby's organs; many people notice nausea and tiredness.
- Second trimester (weeks 14–27): often the most comfortable stretch; many people feel the first movements around weeks 16–22.
- Third trimester (weeks 28–40+): the baby gains most of their weight. Full term begins at 39 weeks.
Common questions
Why am I "pregnant" before I conceived?
Because the count starts from the first day of your last period, which is easier to know than the conception date. Conception usually happens around week 2.
Is the baby really the size of a fruit?
The comparisons are rough, friendly guides to typical length or weight, not measurements. Every baby grows at their own pace, and your ultrasound gives the best estimate.
What if my cycles aren't 28 days?
The standard count assumes a 28-day cycle. If your cycles are longer or irregular, an early ultrasound may adjust your dates. You can enter that due date above instead. For a cycle-length adjustment, try the due date calculator.
How accurate is my due date?
Only a small share of babies arrive on their due date. Most are born within about two weeks either side of it.