Key takeaways
Calculate your pregnancy week from your LMP or your conception date.
The EDD is an estimate — only 3–5% of babies are born on that exact day.
Each trimester has its own biological milestones and typical discomforts.
Contact your doctor or midwife immediately if you notice any warning signs.
Partner mode shows how to support your partner week by week.
# Pregnancy Weeks Calculator: More Than Just a Due Date
40 weeks Average pregnancy duration
280 days Days of gestation
±14 days EDD margin of error
# How is the pregnancy week calculated?
- The most common method uses the first day of your last menstrual period (LMP) as the starting point.
- 280 days are added to the LMP to obtain the estimated due date (EDD).
- If your cycle differs from 28 days, the EDD is adjusted automatically.
- The conception method subtracts 14 days from the count to approximate the EDD from fertilisation.
- A first-trimester ultrasound can correct gestational age with greater precision.
If your doctor gives a different date from the one calculated here, it is most likely due to an irregular cycle or a first-trimester ultrasound correction. Both dates are valid.
# The three trimesters of pregnancy
| Trimester | Weeks | Key milestone | Mother's body |
|---|---|---|---|
| 1st | 1 – 12 | Organ formation | Nausea, fatigue, implantation |
| 2nd | 13 – 26 | Foetal movements, morphology scan | Energy restored, bump visible |
| 3rd | 27 – 40 | Lung maturation, engagement | Pelvic pressure, birth preparation |
# Biological milestones week by week
| Week | Approx. size | Biological milestone | What the mother feels |
|---|---|---|---|
| 4 | ~1 mm | Implantation in the endometrium | Light spotting possible |
| 8 | ~18 mm | Heart beats 150–170 times/min | Nausea at its peak |
| 12 | ~55 mm | Main organs formed | Miscarriage risk drops sharply |
| 20 | ~25 cm | Baby can hear voices clearly | Morphology ultrasound |
| 28 | ~37 cm | Sleep and wake cycles | Third trimester begins |
| 36 | ~47 cm | Lungs nearly mature | Head engages in pelvis |
| 40 | ~50 cm | Ready to be born | EDD: estimated due date |
# Common symptoms by trimester
First trimester (wks 1–12)
The phase of greatest hormonal change.
- Nausea and vomiting, especially in the mornings
- Extreme fatigue and drowsiness
- Breast tenderness
- Frequent urination
- Mood swings
Second trimester (wks 13–26)
The trimester most mothers feel best in.
- Nausea subsides
- Energy levels improve
- Visible bump from around week 18–20
- First foetal movements (wks 18–22)
- Increasing heartburn
Third trimester (wks 27–40)
Preparation for birth.
- Pelvic pressure and back pain
- Braxton Hicks contractions
- Swollen feet and ankles
- Difficulty sleeping
- Baby engagement (wks 36–38)
# Warning signs that require immediate medical attention
- Heavy vaginal bleeding at any week: seek medical attention immediately.
- Regular contractions before week 37: risk of preterm labour.
- Loss of amniotic fluid: ruptured membranes — go to the emergency room.
- Severe headache with blurred vision: possible pre-eclampsia.
- No foetal movements after week 20: an urgent warning sign.
# Essential medical appointments
- Week 8–12: first ultrasound and first-trimester blood tests.
- Week 12: first-trimester combined screening (nuchal translucency + blood panel).
- Week 18–22: morphology scan (20-week scan).
- Week 24–28: glucose tolerance test (GCT / O'Sullivan).
- Week 36: growth scan and Group B Streptococcus culture.
- LMP (Last Menstrual Period)
- The first day of your last period. Used as the reference point for calculating gestational age.
- EDD (Estimated Due Date)
- The expected delivery date, calculated by adding 280 days to the LMP.
- Amniotic Fluid
- The fluid surrounding the baby in the uterus. It protects the foetus, regulates temperature and allows movement.
- Mucus Plug
- A thick secretion that seals the cervix during pregnancy. Losing it indicates labour is approaching.
- Pre-eclampsia
- A pregnancy complication characterised by high blood pressure and organ damage. Requires urgent medical attention.