Pregnancy Week Calculator
Find out exactly how many weeks and days pregnant you are, with a progress bar and development milestones.
About this calculator
Enter your last menstrual period or estimated conception date to see exactly how far along you are, in weeks and days, along with which trimester you're in and a visual progress bar toward the standard 40-week mark. General development milestones for your current stage are shown for context; every pregnancy progresses differently.
Pregnancy weeks are counted the way ages are: when you're 12 weeks and 3 days pregnant, you've completed 12 weeks and are in your 13th week. Apps and books sometimes differ by one because some say "week 13" where others say "12 weeks", which is a common source of confusion. Your provider will usually describe it as completed weeks plus days, such as 12w3d.
Converting weeks to months isn't exact, because months have between 28 and 31 days while weeks are always 7. A common approximation treats the first trimester as months 1 to 3 (through 13 weeks), the second as months 4 to 6 (14 to 27 weeks), and the third as months 7 to 9 (28 weeks to birth). The development notes shown for each stage are general; every pregnancy is different, and your provider is the best source for how yours is progressing.
Frequently asked questions
- Why does pregnancy last 40 weeks if it's only 9 months?
- 40 weeks works out to roughly 9.2 months, and, importantly, that count starts from your last menstrual period, about two weeks before conception actually occurs. So a pregnancy is really about 38 weeks from conception, but 40 weeks is the standard way it's measured and discussed.
- What's the difference between LMP-based and conception-based dating?
- LMP-based dating (the medical standard) starts counting from your last period. Conception-based dating starts about 2 weeks later, from the estimated day of conception. This calculator supports either as a starting point and converts appropriately.
- How many months pregnant am I at 20 weeks?
- About four and a half months. At 20 weeks you're halfway to the standard 40-week due date, and you're in the fifth month by most common charts.
- When does week 1 of pregnancy start?
- Week 1 starts on the first day of your last period, before conception has happened. That's why you're typically considered about 4 weeks pregnant around the time a period would be missed.