How many weeks pregnant am I?
Find out how many weeks and days pregnant you are today, which trimester you’re in and what’s coming up next. Start from your last period, your due date, conception or an IVF transfer.
An estimate, not a diagnosis. An early ultrasound is the most accurate way to date a pregnancy, and your midwife or doctor may change your due date after one. Nothing you enter leaves this device.
How pregnancy weeks are counted
- From the last period: week 1 starts on the first day of your last menstrual period, about 2 weeks before conception. So the first two “weeks” happen before you’re actually pregnant.
- Weeks and days: “12 weeks 3 days” (often written 12+3) means 12 full weeks and 3 days have passed since that date.
- From a due date: the calculator counts back 280 days (40 weeks) to find day 0, then counts forward to today.
- After IVF: the embryo’s age sets the dates. Transfer of a day-5 embryo counts as 2 weeks 5 days pregnant; a day-3 embryo as 2 weeks 3 days.
Trimesters
- First trimester: up to 13 weeks 6 days. Tiredness and nausea are common; this is when dating and screening tests happen.
- Second trimester: 14 weeks to 27 weeks 6 days. First movements are often felt around this time.
- Third trimester: 28 weeks to birth. Term starts at 37 weeks; the due date is 40 weeks.
Key dates in pregnancy (Australia)
- Dating ultrasound: 8 to 14 weeks, mainly to confirm the due date, especially if your period dates are unsure.
- NIPT (non-invasive prenatal testing): an optional blood test from 10 weeks that screens for some chromosome conditions. It isn’t covered by Medicare, so there’s usually a private cost.
- Combined first trimester screening: an optional blood test plus a scan of the back of the baby’s neck, at about 11 to 13 weeks.
- Morphology (anatomy) scan: 18 to 20 weeks, to check how the baby and placenta are developing.
- Whooping cough vaccine: ideally 20 to 32 weeks of every pregnancy. The flu vaccine can be given at any stage.
- Glucose tolerance test: 24 to 28 weeks, to check for gestational diabetes. Some people are tested earlier.
- RSV vaccine: from 28 weeks, preferably by the end of 36 weeks, to protect the baby in the first months of life.
- Term: babies born from 37 weeks are term. The due date is 40 weeks.
When to get help
Call your midwife, GP, maternity unit or 000 straight away for:
- Bleeding from the vagina, or fluid leaking
- Strong or ongoing tummy pain
- A bad headache, blurred vision, or sudden swelling of the face or hands
- A fever, or feeling very unwell
- Your baby moving less than usual, or a change in the pattern of movements, later in pregnancy
In Australia, the free Pregnancy, Birth and Baby helpline is 1800 882 436 (7am to midnight AET, every day).
Common questions
How do I work out how many weeks pregnant I am?
Count from the first day of your last period: the number of full weeks since then is how many weeks pregnant you are. If you know your due date, count back 40 weeks to find the start, then forward to today. This calculator does both.
Why does pregnancy count from my last period, not conception?
Most people know when their period started but not exactly when they conceived. Counting from the last period is a simple standard, so “weeks pregnant” is about 2 weeks more than the baby’s actual age.
When does the second trimester start?
At 14 weeks. The first trimester runs to 13 weeks 6 days, the second from 14 to 27 weeks 6 days, and the third from 28 weeks to birth.
How many weeks is full term?
Babies born from 37 weeks are term. The due date is 40 weeks, and most babies are born between 37 and 42 weeks.
Is 40 weeks the same as 9 months?
Roughly. 40 weeks from the last period is about 9 months and 1 week, but because counting starts 2 weeks before conception, the baby has been growing for about 38 weeks.
Sources
- ACOG Committee Opinion 700: Methods for estimating the due date (2017, reaffirmed). 280 days from LMP; IVF: transfer + 263 days (day-3 embryo) or + 261 days (day-5 embryo); when an early scan should change the due date
- Australian Government Department of Health: Pregnancy timeline fact sheet (2025). dating scan 8 to 14 weeks; morphology 18 to 20 weeks; glucose test 24 to 28 weeks
- ADIPS 2025 consensus recommendations on gestational diabetes (Med J Aust). 75 g glucose tolerance test at 24 to 28 weeks; earlier testing for some
- RACGP, Australian Family Physician: Noninvasive prenatal testing. NIPT from 10 weeks; combined first trimester screening at 11 to 13 weeks
- Australian Immunisation Handbook: vaccines recommended in pregnancy. whooping cough ideally 20 to 32 weeks; RSV (Abrysvo) 28 to 36 weeks; flu vaccine at any stage
- Pregnancy, Birth and Baby: checkups, scans and tests