Pregnancy Week Calculator
How many weeks pregnant you are, with baby size and growth charts. Free, private and instant.
How to use the Pregnancy Week Calculator
- Choose work out from my: Last period date or Due date.
- Answer any extra questions that appear for your choices.
- Press Calculate to get an instant result with a colour scale, chart and plain-English explanation.
About the Pregnancy Week Calculator
Find out how many weeks and days pregnant you are from your last period or due date. The calculator compares your baby’s size to a fruit, shows typical length and weight, and explains what usually happens this week, with growth charts for the whole pregnancy.
Also known as: how many weeks pregnant am I, gestational age calculator, pregnancy week by week, weeks pregnant calculator.
Worked example
Dates in this example are worked out as if today were 5 Nov 2026.
- Work out from my: Last period date
- First day of your last period: 18 Jul 2026
You are: 15 weeks + 5 days (Second trimester). You are 15 weeks 5 days pregnant. Your baby is about the size of an apple, roughly 10 cm long. Hair and eyebrows grow. The sex may be visible on a scan. Energy often returns.
- Baby is about the size of: an apple
- Length: 10 cm
- Weight: 79 g
- Due date: 24 Apr 2027
Formula and cut-offs
Gestational age = today - first day of last period (or due date - 280 days). Weeks = days / 7. Baby length and weight are typical averages interpolated between published weekly values.
Frequently asked questions
How many weeks pregnant am I?
Count the days since the first day of your last period and divide by 7. This calculator does it automatically.
How big is my baby at 20 weeks?
About the size of a banana, around 25 cm from head to heel and about 300 g.
When is the baby full term?
A pregnancy is full term from 37 weeks, and the due date is at 40 weeks.
Sources and references
- ACOG Committee Opinion 700 - Methods for estimating the due date
- Institute of Medicine (2009) - Weight Gain During Pregnancy: Reexamining the Guidelines
- NHS - Pregnancy guide
Written and checked by the MediHub editorial team against the sources above. Read how we build and review our calculators.
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Last updated . This calculator is for education only and is not medical advice. See the medical disclaimer.