Pregnancy Timeline: How to Accurately Calculate Weeks into Months

A standard pregnancy timeline is around 40 weeks. It is divided into 3 trimesters:

1. First Trimester (from weeks 1-12)

What happens: All major organs and systems start to develop, including the brain and spinal cord.

2. Second Trimester (from weeks 13-26)

What happens: The fetus grows rapidly, and the baby's ability to hear and move its eyes starts to develop.

3. Third Trimester (from weeks 27-40)

What happens: All the organs mature, with lungs still developing. The baby often settles into a head-down position in preparation for birth.

Many expecting couples find it confusing to convert pregnancy weeks into months, but do not worry, we have curated the best methods for your easy understanding. However, to accurately track your pregnancy, contact the best gynecologist in Kolkata.

Read Also: How Much Does Delivery Cost In Kolkata? A Breakdown of Maternity Packages

How to Calculate Pregnancy Weeks to Months | The Methods

Find some simple methods here

1. Divide by 4 Weeks per Month

Treat each month as exactly 4 weeks (28 days).​ Then, divide the total weeks by 4.

For Example

• For 20 weeks, 20 ÷ 4 = 5 months
• For 25 weeks, 25 ÷ 4 = 6.25 months

2. Fixed Weekly Blocks per Month (The Easy Method)

Group weeks into standard lunar-style months of 4 weeks each. Note, the real calendar methods are a little longer.

Group the pregnancy into blocks like this:

• Weeks 1–4 = Month 1
• Weeks 5–8 = Month 2
• Weeks 9–12 = Month 3
• and so on, until Weeks 37–40 = Month 10

The simple trick to “pregnancy months”: Just count how many full 4-week blocks have passed and note how many extra weeks are left over.

Example 1:

13 weeks pregnant:

12 weeks = 3 full months

• 1 extra week

 → You’re 3 months and 1 week pregnant.

Example 2:

27 weeks pregnant:
24 weeks = 6 full months

• 3 extra weeks

 → You’re 6 months and 3 weeks pregnant.

3. Manual Calendar Formula

Subtract months and days from the last menstrual period (LMP) to today, then multiply months by 4 ⅓ (4.333 average weeks each month) and add week equivalents from days.​

Formula: Gestational age = (months difference × 4.333) + (days ÷ 7).

Example

LMP: January 1
Today: March 1
Time passed: 2 months, 0 days

Calculation:
(2 × 4.33) + (0 ÷ 7) ≈ 8.66 weeks
That’s roughly 8–9 weeks, or about 2 months pregnant.

Note: These do not tell the exact month or week. Consult your doctor for the correct pregnancy guidelines and due date.

Read Also: High-Risk Pregnancy Specialists in Kolkata: What Mothers Should Know

Refer to This Week-to-Month Pregnancy Table | No Calculation Required

If you are confused about other methods, you can take this chart as a reference to know the pregnancy week or month.

Pregnancy Trimester	Approximate Month	Weeks
First	1	1-4
First	2	5-8
First	3	9-13
Second	4	14-17
Second	5	18-21
Second	6	22-26
Third	7	27-30
Third	8	31-35
Third	9/10	36-40

Quick Review

• 21 Weeks of Pregnancy in Months = around 5 months pregnant.
• 31 weeks pregnant in months = around 7 months pregnant.

Read Also: Painless Normal Delivery in Kolkata: Cost, Benefits, and Process Explained

How Do You Calculate Your Due Date?

The exact due date will be confirmed by your doctor based on ultrasound results. There are also many methods to determine your due date; one of the easiest ways is

• Note down the date of your LMP.
• Add seven days.
• Count back 3 months.
• Add 1 year.

For Example

• LMP: June 10, 2025
• Add 7 days: June 17, 2025
• Go back 3 months: March 17, 2025
• Add 1 year: March 17, 2026

There are many online pregnancy due date calculators that require you to enter your LMP and will calculate the due date for you.

What Does Gestational Age Mean?

Gestational age estimates how far along you are in your pregnancy. Your doctor uses the gestational age in weeks (rather than months) to plan your care during pregnancy. Gestational age is a combination of weeks and days. 

For Example

22 weeks and 3 days pregnant, you might see this same figure written as 22 3/7 or referred to as 22 weeks of gestation.

Note: Gestational age describes your pregnancy, not the fetus.

Gestational Age Vs Fetal Age

• Gestational age measures pregnancy length from the 1st day of the LMP. 
• Fetal age tracks the actual time since conception.

Typically, fetal age is about 2 weeks shorter.

Symptoms I Can Experience Trimester-wise

Not everyone will experience these symptoms; however, you can expect these experiences in the three trimesters.

1. First Trimester Symptoms

• Fatigue
• Morning sickness
• Tender and swollen breasts
• Constipation
• Mood swings
• Headache
• Food cravings
• Food aversions
• Heartburn

2. Second Trimester Symptoms

• Body and muscle pain
• Weight gain
• Darkening of skin around your nipple
• Developing a linea nigra. A dark line that develops on your stomach during pregnancy. It generally extends from the belly button to your pubic area.
• Patches of dark skin

3. Third Trimester Symptoms

• Shortness of breath
• Lower back pain
• Frequent pee
• Trouble sleeping
• Leaking of colostrum, the first form of breast milk from the breast
• Signs of labor, such as uterine contractions or loss of the mucus plug
• The fetus drops into the pelvis, preparing for birth

Conclusion

A pregnancy is when a fetus grows inside your womb, lasting about 40 weeks. This is split into 3 trimesters that each last around 13 weeks. During your pregnancy journey, it is important to follow all your doctor's advice and go for timely visits. This will ensure that the fetus is growing in a healthy way for a successful pregnancy. 

Looking for the best gynecological hospital? 

Contact RIS Multispeciality Hospital in Kolkata for both accessible and affordable pregnancy care.

FAQs

Q1: Why do I not feel pregnant at 6 weeks?
A: Most pregnancy symptoms don’t begin until 4 to 6 weeks after conception. However, it’s possible to not experience any symptoms during the first trimester of pregnancy due to individual hormone variation.

Q2: What is the normal timeline of pregnancy?
A: Pregnancy is divided into 3 stages known as trimesters: First trimester (1 to 13 weeks), second trimester (14 to 26 weeks), and third trimester (27 to 40 weeks).

Q3: When should I announce my pregnancy?
A: There is no fixed timeline as such to announce your pregnancy. However, many prefer to wait until around week 13 because of the lower risk of miscarriage.

Q4: How many months is 7 weeks pregnant?
A: It normally means the second month of pregnancy.