The short answer
4 weeks = 1 month
At 4 weeks pregnant, you are about 1 month pregnant — in month 1 of your pregnancy and in your first trimester.
Not sure of your week? Use the pregnancy week calculator to find it from your last period, due date or conception date.
Implantation is wrapping up and a sensitive home test may already turn positive. The embryo is about the size of a poppy seed, and the neural tube — the start of the brain and spinal cord — is beginning to form.
About the size of a poppy seed
size comparison
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crown to rump
—
average weight
The blastocyst has split into two groups of cells: an inner cluster that becomes the embryo and an outer layer that becomes the placenta. Three distinct cell layers are being laid down, and each one is already assigned to a job — skin and nerves, muscle and bone, or gut and lungs. The yolk sac, which feeds the embryo until the placenta takes over, is forming alongside it.
Sizes and weights are averages — healthy babies vary widely, and your scan measurements are what count.
Most people feel nothing different at all this week, and that is completely normal. Some notice light spotting from implantation or mild cramping that is easy to mistake for a period on its way. Rising hCG is what a home test picks up, and it doubles roughly every two to three days from here.
Common symptoms this week
252
days to go
36
weeks to go
28
days so far
At 4 weeks 0 days you are 28 days into a 280-day pregnancy, which leaves 252 days — 36 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: 70 days until the second trimester (14 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 4 falls in month 1, in the first 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 — 4+3 or 4w3d, 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 |
|---|---|---|---|
| 4 weeks 0 days (this page) | 4+0 | 28 | 252 |
| 4 weeks 1 day | 4+1 | 29 | 251 |
| 4 weeks 2 days | 4+2 | 30 | 250 |
| 4 weeks 3 days | 4+3 | 31 | 249 |
| 4 weeks 4 days | 4+4 | 32 | 248 |
| 4 weeks 5 days | 4+5 | 33 | 247 |
| 4 weeks 6 days | 4+6 | 34 | 246 |
At 4 weeks pregnant, you are about 1 month pregnant — in month 1 of your pregnancy and in your first trimester. Months of pregnancy are counted as uneven 4–5 week buckets so that the full 40 weeks fits into 9 calendar months.
4 weeks is in the first trimester, which runs from week 0 through 13 weeks 6 days. The second trimester begins at 14 weeks 0 days.
About 36 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 4 weeks 0 days you are 28 days into a 280-day pregnancy, so there are 252 days left until the 40-week mark — that's 36 weeks. The count drops by one for each day you move through week 4.
4 weeks is 28 days, counted from the first day of your last menstrual period (4 × 7 = 28). Add the days into your current week for the exact figure — for example 4 weeks 3 days is 31 days.