Why weeks don’t convert neatly into months
A calendar month has 28 to 31 days – about 4.3 weeks, not 4. So 40 weeks is not 10 months, and not exactly 9 either: from your LMP to your due date is 9 calendar months and about 7 days. Because of this, different books and apps place the month boundaries differently. The most common convention, used in this calculator, gives months 3 and 5 an extra week.
Pregnancy weeks to months chart
| Month | Weeks | Trimester |
|---|---|---|
| Month 1 | 0–4 | 1st |
| Month 2 | 5–8 | 1st |
| Month 3 | 9–13 | 1st |
| Month 4 | 14–17 | 2nd |
| Month 5 | 18–22 | 2nd |
| Month 6 | 23–27 | 2nd |
| Month 7 | 28–31 | 3rd |
| Month 8 | 32–35 | 3rd |
| Month 9 | 36–40 | 3rd |
Quick conversions: 12 weeks ≈ end of month 3; 16 weeks ≈ month 4; 20 weeks ≈ month 5; 24 weeks ≈ month 6; 28 weeks ≈ start of month 7; 32 weeks ≈ month 8; 36 weeks ≈ month 9.
Is pregnancy 9 months or 10?
Both answers appear, and both have a logic. If you count four-week “lunar” months, 40 weeks is exactly 10 months. If you count calendar months from your LMP, it’s just over 9. In India, people commonly speak of the “9th month” as the final stretch, which matches the calendar-month view – and the one this calculator uses.
Your results also show “months and days completed” by the calendar – useful for forms that ask “How many months pregnant?”.
Read about each month in detail: month 1, month 2, month 3, month 4, month 5, month 6, month 7, month 8, month 9.
Frequently asked questions
How many months is 20 weeks pregnant?
20 weeks is in the 5th month of pregnancy – about 4 calendar months and 2 weeks since your LMP.
How many weeks is 6 months pregnant?
The sixth month covers roughly weeks 23 to 27.
How many months is 30 weeks pregnant?
30 weeks is in the 7th month (weeks 28–31).
When does the 9th month of pregnancy start?
At about 36 weeks. It runs until birth.
Why do apps show different months for the same week?
Because weeks don’t divide evenly into months, there is no single universal chart. Always rely on weeks and days for medical purposes.
Medical disclaimer: The results and information on this page are estimates for general education only. They are not a diagnosis and do not replace advice from your gynaecologist, obstetrician or midwife. If you have pain, bleeding, reduced baby movements or feel unwell, contact your doctor or call 108 immediately. Read the full disclaimer.