DueDateCalcPregnancy Timeline — Week by Week, 1 to 40
A condensed map of a typical pregnancy: what is developing, which screening windows open, and where the trimester boundaries fall.
Every pregnancy differs, and sizes below are rough averages meant for orientation only. Your provider's scans and measurements describe your pregnancy — this table does not.
First trimester: weeks 1–13 (to 13w6d)Second: 14–27 (to 27w6d)Third: 28–40+
| Week | What typically happens | Approx. size |
|---|---|---|
| Week 1 | Counting starts: this 'week 1' begins with your last period, before conception has happened. | — |
| Week 2 | Still pre-conception in a typical cycle; the body prepares an egg. | — |
| Week 3 | Fertilisation usually occurs around the end of this week (day 14 in a 28-day cycle). | ~Day 14 |
| Week 4 | The fertilised egg implants in the uterus; a missed period may be the first sign. | Missed period |
| Week 5 | The neural tube — which becomes the brain and spine — is forming. Folic acid matters now. | ~2 mm |
| Week 6 | A tiny heartbeat may be detectable on an early scan late this week or next. | ~4 mm |
| Week 7 | Arm and leg buds appear; facial features begin. | ~1 cm |
| Week 8 | Most major organs have begun forming; the embryo is now often called a fetus around week 9–10. | ~1.6 cm |
| Week 9 | Fingers and toes are distinct; reflexes start. | ~2.3 cm |
| Week 10 | All essential organs are present in basic form; risk of miscarriage begins to fall. | ~3 cm |
| Week 11 | The fetus can make small movements; the first-trimester screening window opens (11–14 weeks). | ~4 cm |
| Week 12 | Reflexes develop; the fetus may start to swallow. | ~5–6 cm |
| Week 13 | Fingerprints are forming; vocal cords develop. | ~7 cm |
| Week 14 | End of the first trimester (13w6d). The fetus can open and close its fingers. | ~7–8 cm |
| Week 15 | Hair pattern is set; the fetus can make facial expressions. | ~9 cm |
| Week 16 | You may begin to feel a bump; many people share their news around now. | ~10 cm |
| Week 17 | The fetus can yawn and stretch; sex organs are distinguishable on scan for many. | ~11 cm |
| Week 18 | Quickening — the first felt flutters of movement — may begin, often later for first pregnancies. | ~12 cm |
| Week 19 | The anatomy (anomaly) scan window opens at 18 weeks: a detailed check of development. | ~14 cm |
| Week 20 | Hair (lanugo) covers the body; the fetus can hear some sounds. | ~15 cm |
| Week 21 | Halfway by the calendar. The anatomy scan is commonly done around now (18–22 weeks). | ~25 cm (head–heel) |
| Week 22 | The fetus responds to sounds; a sleep–wake pattern emerges. | ~26 cm |
| Week 23 | Taste buds are working; the fetus swallows amniotic fluid. | ~27 cm |
| Week 24 | Eyes begin to open; lungs continue maturing. | ~28 cm |
| Week 25 | The glucose screening window (24–28 weeks) typically falls around now. | ~35 cm |
| Week 26 | End of the second trimester (27w6d). Survival outside the womb is increasingly likely with care. | ~36 cm |
| Week 27 | Third trimester begins. The fetus gains weight steadily from here. | ~37 cm |
| Week 28 | Brain development is rapid; the fetus practices breathing movements. | ~38 cm |
| Week 29 | Movements may feel stronger; kicks are often counted around this stage — follow your provider's guidance. | ~40 cm |
| Week 30 | Lungs are maturing; the fetus may settle head-down. | ~42 cm |
| Week 31 | Fat stores build; skin becomes smoother. | ~43 cm |
| Week 32 | The fetus is usually head-down by now; your provider may check position. | ~45 cm |
| Week 33 | Growth continues; space gets tight, so movements feel like rolls more than kicks. | ~46 cm |
| Week 34 | Considered early term from 37 weeks. Most organs are mature. | ~47 cm |
| Week 35 | The fetus practices grasping; the brain keeps developing rapidly. | ~48 cm |
| Week 36 | Full term approaches; the average baby now weighs around 3–3.5 kg, with wide variation. | ~49 cm |
| Week 37 | The estimated due date — only around 5% of babies arrive on this exact day. | ~50 cm |
| Week 38 | Many providers discuss monitoring and induction options as 41 weeks passes. | ~51 cm |
| Week 39 | Most guidelines recommend delivery by around 42 weeks; your provider will advise. | ~51 cm |
Please read: This calculator gives estimates only — it is not medical advice and cannot diagnose or date a pregnancy with certainty. Only around 5% of babies arrive on their estimated due date, and most arrive within a week or so either side. Ultrasound dating performed by a clinician takes precedence over any calculator result. Always confirm your dates, screening windows and care plan with your healthcare provider. All dates are processed locally in your browser; nothing you enter is uploaded or stored.
The windows worth putting in a calendar
Three screening windows recur in many care systems: a first scan and screening window around weeks 11–14, the anatomy scan around weeks 18–22, and glucose screening around weeks 24–28. They are described here as typical windows only — schedules vary by country, provider and individual circumstances, so confirm your own appointments with your healthcare provider.
Want these windows as dates for your own pregnancy? The due date calculator turns any due date into a personal timeline.