The short answer
18 weeks = 5 months
At 18 weeks pregnant, you are about 5 months pregnant — in month 5 of your pregnancy and in your second trimester.
Not sure of your week? Use the pregnancy week calculator to find it from your last period, due date or conception date.
The anatomy scan window (18–22 weeks) opens now. If you haven’t felt movement yet, those first flutters could arrive any day.
About the size of a bell pepper
size comparison
14.2 cm
crown to rump (5.6 in)
190 g
average weight (6.7 oz)
Nerves are becoming coated in myelin, an insulating layer that speeds up signals and continues developing for a year after birth. The genitals are formed enough to see on ultrasound, and in girls the uterus and fallopian tubes are in place. The fetus yawns, hiccups and rolls, and its unique fingerprints are complete.
Sizes and weights are averages — healthy babies vary widely, and your scan measurements are what count.
Lying on your back may start to feel uncomfortable or make you lightheaded, because the uterus can press on a major vein. Blood pressure is often at its lowest point in pregnancy around now, so dizziness is common. Backache and leg cramps often become part of daily life.
Common symptoms this week
154
days to go
22
weeks to go
126
days so far
At 18 weeks 0 days you are 126 days into a 280-day pregnancy, which leaves 154 days — 22 weeks — until 40 weeks. That number drops by one for every day you move through this week. Remember the due date is an estimate: only about 1 in 20 babies is born on it, and most arrive within two weeks on either side.
Next milestone: 14 days until the halfway point (20 weeks 0 days).
A calendar month averages about 4.3 weeks — not 4 — so you can't just divide your week number by four. Instead, months of pregnancy are counted as uneven buckets of 4 to 5 weeks, arranged so the full 40 weeks fits into 9 calendar months. Week 18 falls in month 5, in the second trimester.
Your care team will always use weeks and days rather than months, because screening windows and term definitions are set by exact week — months are just the everyday shorthand. For the full conversion, see the weeks to months chart, or go the other way with the months-to-weeks guide.
Your notes will show a week and a day — 18+3 or 18w3d, for example. Pick the exact day you are on for its own day count, countdown and month answer.
| Week + day | Shorthand | Days pregnant | Days to go |
|---|---|---|---|
| 18 weeks 0 days (this page) | 18+0 | 126 | 154 |
| 18 weeks 1 day | 18+1 | 127 | 153 |
| 18 weeks 2 days | 18+2 | 128 | 152 |
| 18 weeks 3 days | 18+3 | 129 | 151 |
| 18 weeks 4 days | 18+4 | 130 | 150 |
| 18 weeks 5 days | 18+5 | 131 | 149 |
| 18 weeks 6 days | 18+6 | 132 | 148 |
At 18 weeks pregnant, you are about 5 months pregnant — in month 5 of your pregnancy and in your second trimester. Months of pregnancy are counted as uneven 4–5 week buckets so that the full 40 weeks fits into 9 calendar months.
18 weeks is in the second trimester, which runs from 14 weeks 0 days through 27 weeks 6 days. The third trimester begins at 28 weeks 0 days.
About 22 weeks until the 40-week mark — though only about 1 in 20 babies arrives exactly on the due date. Most are born within two weeks on either side of it.
At 18 weeks 0 days you are 126 days into a 280-day pregnancy, so there are 154 days left until the 40-week mark — that's 22 weeks. The count drops by one for each day you move through week 18.
18 weeks is 126 days, counted from the first day of your last menstrual period (18 × 7 = 126). Add the days into your current week for the exact figure — for example 18 weeks 3 days is 129 days.