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Updated February 25, 2015.
Question: How many months pregnant am I?
The average pregnancy lasts 40 weeks from the day of the last normal menstrual period. Most physicians and midwives use the gestation calculation of weeks rather than months because it is more specific.
Answer: We talk a good game about there being nine months of pregnancy. But if you look at it mathematically, there are an average of 40 weeks in a normal pregnancy.
If you calculate a month as being four weeks, that makes 10 months of pregnancy in every 40 weeks. The problem with this calculation is that it has 28 day months, which is not the norm in our calendar months.
There is also the issue of when you actually are pregnant. Now this honestly doesn't really matter much to most people, since that's just how pregnancy is calculated. And, by the time you have a positive pregnancy test, you are four weeks pregnant. Here are some common break downs of the months of pregnancy and their explanations:
Heavy on the 1st Trimester
- Month One: Week 1-6
- Month Two: Week 7-11
- Month Three: Week 12-16
- Month Four: Week 17-20
- Month Five: Week 21-24
- Month Six: Week 25-28
- Month Seven: Week 29-32
- Month Eight: Week 33-36
- Month Nine: Week 37+
This set of weeks assumes that early pregnancy is very important but that you aren't really pregnant those first two weeks.
Heavy on the 3rd Trimester
- Month One: Week 1-4
- Month Two: Week 5-8
- Month Three: Week 9-12
- Month Four: Week 13-16
- Month Five: Week 17-20
- Month Six: Week 21-24
- Month Seven: Week 25-28
- Month Eight: Week 29-32
- Month Nine: Week 33+
This set of weeks counts every moment from the last normal menstrual cycle and considers the fact that some women have their babies earlier than 40 weeks.
Interested in figuring out when you got pregnant? Try the backwards pregnancy calculator. Source:
Obstetrics: Normal and Problem Pregnancies. Gabbe, S, Niebyl, J, Simpson, JL. Fifth Edition.