Also written 21+3 or 21w3d
The short answer
21 weeks 3 days = 5 months
At 21 weeks 3 days pregnant you are about 5 months pregnant — day 150 of your pregnancy, in month 5 and your second trimester.
Not sure of your exact week and day? The pregnancy week calculator works it out from your last period, due date or conception date.
130
days to go
18
whole weeks + 4d
54%
complete
You are 150 days into a 280-day pregnancy, so there are 130 days — 18 weeks and 4 days — left until you reach 40 weeks. Bear in mind that 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: 46 days until the third trimester (28 weeks 0 days).
Months of pregnancy are counted in uneven buckets of 4 to 5 weeks, arranged so that the full 40 weeks fits into 9 calendar months. Week 21 sits inside month 5, and it stays there for all seven days of the week — so 21 weeks 0 days and 21 weeks 3 days are both "5 months pregnant".
If you want the strict calendar answer instead, divide by the real length of a month rather than by four: 150 days ÷ 30.4375 days per month = 4.9 calendar months. That figure drifts from the bucket-based month number, which is exactly why your care team sticks to weeks and days.
The days part matters clinically even when the month doesn't. Screening windows, term definitions and induction timing are all set by exact week and day — full term starts at 39 weeks 0 days, not "9 months". See the full weeks to months chart for every week.
The fetus is entering a phase of steady weight gain, and movements are becoming stronger and easier to notice.
Read the full week 21 breakdown →
| Week + day | Months pregnant | Days pregnant | Days to go |
|---|---|---|---|
| 21 weeks | about 5 months | 147 | 133 |
| 21 weeks 1 day | about 5 months | 148 | 132 |
| 21 weeks 2 days | about 5 months | 149 | 131 |
| 21 weeks 3 days (you) | about 5 months | 150 | 130 |
| 21 weeks 4 days | about 5 months | 151 | 129 |
| 21 weeks 5 days | about 5 months | 152 | 128 |
| 21 weeks 6 days | about 5 months | 153 | 127 |
At 21 weeks 3 days pregnant you are about 5 months pregnant — day 150 of your pregnancy, in month 5 and your second trimester. Months of pregnancy are counted as uneven 4–5 week buckets so the full 40 weeks fits into 9 calendar months, which is why the extra 3 days doesn't change your month number.
"21+3" is the shorthand your midwife or doctor uses for 21 weeks 3 days — the number before the plus is completed weeks, the number after it is completed days into the current week. You may also see it written 21w3d. Both mean exactly the same thing.
21 weeks 3 days is 150 days, counted from the first day of your last menstrual period (21 × 7 = 147, plus 3). That leaves 130 days — 18 weeks and 4 days — until the 40-week mark.
About 18 weeks and 4 days until 40 weeks. Only about 1 in 20 babies arrives exactly on the estimated due date, though — most are born within two weeks on either side of it.
21 weeks 3 days 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.