Weeks to months of pregnancy: calculator and full table
Calculadora: semanas a meses de embarazo
Introduce las semanas que llevas y te digo de cuántos meses estás
I am 28 weeks — how many months is that? If that question has brought you here, you are in good company ❤️. It is one of the first things everyone asks once the test comes back positive, and the honest answer is: pregnancy is counted in weeks and trimesters, not in months. Months are just how we talk about it in real life, so any conversion you see is a helpful guide rather than an exact number.
Below is a weeks-to-months calculator that works it out for you in a second, followed by the full chart and the handful of things that actually trip people up (like why one website says 24 weeks is 5 months and another says 6).
Weeks to months: the quick calculator
Enter how many weeks pregnant you are (plus the extra days if you know them) and the calculator above will tell you:
- Which month you are in, from 1 to 9, using the most common conversion.
- Which trimester you are in.
- How many weeks are left until week 40, when pregnancy is considered full term.
If you would rather just look it up, the complete chart is further down the page.
The weeks-to-months chart
This is the conversion most people use. Just keep in mind that months are not a medical standard here — the official measurements are weeks and trimesters.
| Month of pregnancy | Weeks | Trimester |
|---|---|---|
| Month 1 | Weeks 1 to 4 | First |
| Month 2 | Weeks 5 to 8 | First |
| Month 3 | Weeks 9 to 13 | First |
| Month 4 | Weeks 14 to 17 | Second |
| Month 5 | Weeks 18 to 22 | Second |
| Month 6 | Weeks 23 to 27 | Second |
| Month 7 | Weeks 28 to 31 | Third |
| Month 8 | Weeks 32 to 35 | Third |
| Month 9 | Weeks 36 to 40 | Third |
If you are weeks and days along (say, 12 weeks and 4 days), the month is decided by your completed week: at 12 weeks you are 3 months until you reach week 14, when month 4 starts. Those extra days do not push you into the next month.
Weeks, months and trimesters: three ways to count the same nine months
It sounds like overkill to use three units for one pregnancy, but each one does a different job:
- Weeks are what your midwife and doctor work with. Every scan, blood test and screening is scheduled by week because it is far more precise than counting in months.
- Trimesters group those weeks into three standard blocks, which is how you know what appointments and tests belong to each stage.
- Months are simply how friends and family count it. Convenient, familiar, and — unlike the other two — not standardised.
So it is completely normal for your midwife to say “you are 30 weeks” and your mum to ask “so, seven months?”. Both are right, they are just different rulers.
”How many months is 28 weeks?”: the questions I get asked most
This is the one that fills my inbox. The confusion really kicks in from the fifth month onwards, because that is where the different charts start to disagree. Here are the three bands that cause the most head-scratching.
18 to 22 weeks
You are 5 months (month 5 runs from week 18 to week 22) and firmly in your second trimester. This is usually when you first feel those fluttery movements — and also when your bump starts to make the pregnancy obvious to everyone else.
23 to 27 weeks
You are 6 months (month 6 covers weeks 23 to 27). If you have spotted a chart that calls this 5 months and another that calls it 6, do not worry: it is just a different way of splitting the weeks, not a difference in your actual pregnancy.
28 weeks and beyond
At 28 weeks you are 7 months (month 7 goes from week 28 to week 31) and into your third trimester. From here, most people — midwives included — switch almost entirely to weeks, because the final stretch is monitored week by week.
How the NHS and your midwife count your pregnancy
Here in the UK (and in most countries), your pregnancy is dated from the first day of your last period, not from the day you conceived. That is why the very first two weeks of “pregnancy” happen before you are actually pregnant — you have not ovulated yet.
It also explains why “4 weeks” does not equal “one month since conception”: the dating system deliberately starts about two weeks earlier. Your midwife will normally confirm your official due date at the dating scan (usually between 11 and 14 weeks), because an early scan is more accurate than counting back to your last period. If you have been given a due date, you can also work backwards from it — our pregnancy weeks calculator and the online gestogram do that for you.
Is pregnancy 9 or 10 months?
By calendar months, a full-term pregnancy of around 40 weeks works out to roughly 9 months, which is why nine is the answer almost everyone gives.
The “10 months” version comes from counting in lunar months — four-week blocks. Forty weeks divided into 4-week units is ten of them. Both numbers describe the same pregnancy; they are just using a different month. Medically, the measure that matters is weeks and trimesters, which is exactly what your antenatal care is built around.
When to call your midwife or doctor
Converting weeks to months is nothing to worry about — it is just a bit of maths. But there are signs that do deserve a phone call rather than waiting for your next appointment:
- Vaginal bleeding beyond light spotting, or severe pain in your lower tummy, especially on one side.
- A noticeable reduction or change in your baby’s movements after around 20-22 weeks (or whenever you had started to feel them regularly).
- A high temperature, pain when passing urine, or vomiting that stops you keeping fluids down.
- Any worry about your due date or how many weeks you are — your midwife can recalculate it from your early scan.
If any of these apply, call your midwife or maternity unit rather than waiting. And for anything else that concerns you, your healthcare professional is always the person to ask.
Quick answers: the weeks people look up most
If your week is on this list, here is the short version — no maths needed. It uses the same chart as above, so it will match the month your app shows in most cases.
| Weeks pregnant | Months | Trimester |
|---|---|---|
| 16 weeks | 4 months | Second |
| 20 weeks | 5 months | Second |
| 24 weeks | 6 months | Second |
| 28 weeks | 7 months | Third |
| 32 weeks | 8 months | Third |
| 36 weeks | 9 months | Third |
| 40 weeks | 9 months (full term) | Third |
Two things worth flagging. First, 24 weeks is the classic flashpoint: some charts call it 5 months and some call it 6 — both are just different ways of dividing the same weeks. Second, once you reach week 36, you are into your ninth month and stay there right up to week 40 and beyond; the ninth “month” is the longest because it stretches over the final weeks.
Keep reading: week-by-week guides
Once you know which month you are in, these pages are the natural next step:
- The week-by-week hub takes you through every stage of pregnancy.
- The fertile days calculator helps if you are trying to conceive and want to find your ovulation window.
- The guides for week 1 and week 12 are good starting points.
Frequently asked questions
How many months am I if I am 12 weeks pregnant?
At 12 completed weeks you are 3 months (month 3 covers weeks 9 to 13). From week 14 you move into your fourth month.
How many months is 20 weeks of pregnancy?
20 weeks is 5 months (month 5 runs from week 18 to week 22). You are also in your second trimester.
How many months is 28 weeks of pregnancy?
28 weeks is 7 months (month 7 goes from week 28 to week 31), and you have just entered the third trimester.
How many months is 20 weeks and 5 days?
The days do not change the month: at 20 weeks and 5 days you are still 5 months. You switch to your sixth month when you complete week 23.
How many months is 30 weeks?
30 weeks is 7 months (month 7 runs from week 28 to week 31), within the third trimester.
Is pregnancy 9 or 10 months?
By calendar months, a full-term pregnancy (around 40 weeks) is roughly 9 months. Some people count in 4-week “lunar months” and get about 10 — same pregnancy, different unit. Medically, weeks and trimesters are what is used.
Why do different weeks-to-months charts not match?
Because there is no official chart: months last between 28 and 31 days, and every source splits the weeks its own way. On top of that, pregnancy is dated from your last period, which adds about two weeks before conception. The exact and universal measure is weeks, and months are only a guide from there — for anything specific to your pregnancy, ask your midwife or doctor.
Is the weeks-to-months calculator accurate?
It is accurate enough to orient you: it uses the most common conversion and gives you the month and trimester. It cannot be medically exact, because months have no fixed length. For precision, your midwife works in weeks, usually confirmed by your dating scan.
Sources
- MedlinePlus — Fetal development
- MedlinePlus — Pregnancy
- WHO — Antenatal care (fact sheet)
- ACOG — Methods for estimating the due date
- NHS — Due date calculator
- PubMed — Duration of human pregnancy and its variations (PMID 23922246)
- PubMed — Wilcox et al., timing of conception in the menstrual cycle (PMID 7477165)
I hope this clears up the pregnancy months question ❤️. If you want to dig into your specific week, the week-by-week guides are the place to go. And if you have symptoms you would like to check, you can take our online pregnancy test for some orientation. For a bit of fun, try our finger pregnancy test game — it is just a game, not a real test.
Remember, this content is for information only. If you are pregnant and have any doubts about your pregnancy, always talk to your doctor or midwife — they are the ones who can guide you best ❤️.
