Pregnancy Week Calculator: How to Count Your Weeks and Months Correctly

Your test line came up on Tuesday. By Thursday your mother is telling relatives you are "do mahine ki", your bhabhi insists it is six weeks, and the receptionist at the clinic has written 5+3 on your file. Everyone is describing the same pregnancy. They are just counting from different starting points, and only one of those starting points is the one your doctor will use.

Here is how pregnancy weeks are actually counted in Pakistan, how to turn those weeks into months without the usual argument, and when a scan quietly overrules whatever you worked out at home.

Your pregnancy started before you were pregnant

This is the part that confuses almost everyone. Pregnancy is dated from the first day of your last menstrual period, usually written as LMP on your file. Not from the night you conceived. Not from the day the test turned positive.

In a textbook 28 day cycle you ovulate around day 14. So on the day the egg is actually fertilised, you are already counted as two weeks pregnant. By the time a home test picks up hCG, which is usually a day or two after a missed period, you are sitting at roughly four weeks. That is why the doctor says six weeks when you are certain it has only been a month.

Doctors count this way because the LMP is a date you can remember, while the exact day of conception is guesswork for most women. A full pregnancy is 40 weeks from the LMP, which works out to about 38 weeks of actual growing.

How to count your pregnancy weeks yourself

Take the first day of your last period. Count the days from that date until today, then divide by seven. The whole number is your week, the remainder is your days.

Say your last period started on 1 June and today is 27 August. That is 87 days. Divide by seven and you get 12 with 3 left over, so you are 12 weeks and 3 days pregnant. Your file will show this as 12+3. When a nurse says "twelve plus three" she means exactly this, not twelve months or twelve of anything else.

Working out your due date by hand

The old method is called Naegele's rule and it still works. Take your LMP, add seven days, subtract three months, then add a year.

Using 1 June 2026 again: add seven days to get 8 June, subtract three months to get 8 March, add a year and your estimated due date is 8 March 2027. Only about one baby in twenty arrives on that exact date, so treat it as the middle of a window rather than an appointment.

If your cycle is not 28 days

Naegele's rule assumes a 28 day cycle. Plenty of Pakistani women run 32, 35 or 40 day cycles, and if yours is longer you ovulate later, which means your true dates are behind the standard calculation. A 35 day cycle puts you roughly a week behind. Our pregnancy calculator asks for your cycle length along with your LMP and adjusts for it, then shows your due date, your exact week and day, your trimester and the windows when your scans are due. If you are still trying and want to know when to test, the ovulation calculator works out your fertile days from the same two inputs.

Pregnancy weeks to months chart

Forty weeks is not ten months, even though four weeks feels like a month. A calendar month averages 4.3 weeks, so 40 weeks lands at about nine months and one week. Here is the conversion your family is arguing about.

Month	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

The trimester boundaries matter more than the month boundaries. The first trimester runs weeks 1 to 13, the second covers weeks 14 to 27, and the third starts at week 28. A baby born from 37 weeks onwards is considered term. Before 37 weeks is preterm, and that single number is worth remembering if anyone in your family starts pushing for an early delivery date for convenience.

When the scan overrules your maths

Your home calculation is a good working estimate. The first trimester ultrasound is better. The sonographer measures crown rump length, the distance from the top of the baby's head to the bottom of the spine, and between 8 and 14 weeks that measurement is the most accurate way to date a pregnancy, generally within five to seven days.

The World Health Organization recommends one ultrasound scan before 24 weeks for every pregnant woman, to confirm dates, pick up twins and check for anomalies. Earlier is better for dating, because after about 20 weeks babies grow at different rates and the measurements stop being reliable for calendar purposes.

If your LMP dates and the scan disagree by more than about a week in the first trimester, your doctor will usually redate you to the scan and that becomes your official EDD. Do not argue with the change and do not keep two due dates in your head. Later decisions about induction and growth monitoring all hang off the dated EDD.

This matters most if your periods are irregular, if you have PCOS, if you conceived while breastfeeding, or if you stopped contraceptive pills recently. In all of those cases your LMP maths is shaky and the scan is doing the real work.

What the scans cost in Pakistan

Scan	Typical price (PKR)	When
Dating scan	2,970 at IDC	Weeks 8 to 14
Level I pregnancy scan	3,000 at Chughtai Lab	Any stage
NT scan	3,500 at Chughtai Lab	Weeks 11 to 13+6
Anomaly scan (Level II)	5,000 at Chughtai Lab	Weeks 18 to 22
Transvaginal scan	4,000 at Chughtai Lab	Very early, under 7 weeks

Prices checked in August 2026 and they shift, so call the centre first. Smaller neighbourhood clinics and teaching hospital radiology departments often run well under these figures for a basic obstetric scan, sometimes at Rs 1,200 to Rs 1,800. Government hospitals charge a nominal fee or nothing at all.

What to do at each stage

Knowing your week is only useful if it tells you what to do next. Here is the practical version.

Weeks 4 to 8. Confirm with a home test if you have not already. A midstream pregnancy test runs about Rs 250 and is easier to read than a basic strip, though strips work perfectly well. Book your first antenatal appointment. Start or continue folic acid at 400 mcg daily if you are not on it yet, ideally alongside a proper prenatal multivitamin. Read up on early pregnancy symptoms so you know what is normal.

Weeks 8 to 14. Dating scan, blood group, haemoglobin, blood sugar, thyroid and hepatitis screening. If you want the NT scan for Down syndrome risk, the window closes at 13 weeks and 6 days, so book it rather than assuming there is time.

Weeks 12 onwards. Anaemia is very common in Pakistani pregnancies and this is usually when iron supplements get added. If iron tablets upset your stomach, ask about a gentler formulation rather than quietly stopping.

Weeks 18 to 22. Anomaly scan. This is the detailed one that checks the baby's organs, spine and heart.

Weeks 24 to 28. Glucose tolerance test for gestational diabetes, plus a repeat haemoglobin.

Week 28 onwards. Visits get closer together, monthly to fortnightly and then weekly from 36 weeks. Growth scans if your doctor wants them.

If you would rather not assemble the supplement side piece by piece, the Complete Pregnancy Care pack at Rs 1,720 covers folate, daily nutrition and lactation support in one box, and the fuller Pregnancy and Prenatal Care Combo at Rs 3,474 adds a prenatal multivitamin and non constipating iron for the middle and later months. Everything else sits in our women's health range.

Five counting mistakes worth avoiding

Counting from conception. This puts you two weeks behind everyone else's numbers and causes endless confusion at appointments.

Counting from the positive test. The test only tells you hCG is high enough to detect. It says nothing about how long you have been pregnant.

Treating four weeks as one month. Do that for nine months and you end up a full month ahead of where you actually are.

Ignoring a long cycle. If you run 35 or 40 day cycles, the standard calculation will make you look further along than you are.

Changing your dates after a late scan. Once you have been dated in the first trimester, a growth measurement at 30 weeks does not move your due date. It measures the baby's size, not the calendar.

Keep it simple

Save the first day of your last period in your phone notes right now, along with your usual cycle length. Those two numbers answer almost every dating question anyone will ask you for the next nine months, and they are the first thing a new doctor will want if you switch clinics or travel home for the delivery.

Run them through the pregnancy week calculator whenever you lose track, take the printout or a screenshot to your first appointment, and let the dating scan have the final word. If you are still at the trying stage, our guide on timing conception is the better place to start.

This article is for general information and does not replace antenatal care. Every pregnancy is different, so follow the dates and advice your own doctor gives you.