Pregnancy Baby Week Calculator
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Reviewed by Calculator Editorial Team
This pregnancy baby week calculator helps you determine your current pregnancy week based on your last menstrual period (LMP) or conception date. It also calculates your estimated due date and shows your pregnancy progress in weeks and months.
How to use this calculator
To use this pregnancy week calculator:
- Select whether you want to calculate based on your last menstrual period (LMP) or conception date.
- Enter the relevant date in the date picker.
- Click the "Calculate" button to see your pregnancy week and estimated due date.
- Review the results and progress chart to track your pregnancy journey.
The calculator uses standard pregnancy duration of 40 weeks (280 days) from the first day of your last menstrual period or from conception.
How pregnancy weeks are calculated
Pregnancy weeks are typically counted from the first day of your last menstrual period (LMP). Here's how the calculation works:
Formula
Pregnancy Week = (Current Date - LMP Date) / 7 days
Estimated Due Date = LMP Date + 280 days (40 weeks)
The calculator uses the standard 40-week pregnancy duration. Some sources may use 266 days (38 weeks) from conception, but this calculator follows the more common LMP-based calculation.
Note: Pregnancy durations can vary. This calculator provides an estimate based on average pregnancy length.
Example calculation
Let's say your last menstrual period started on January 1, 2023, and today is March 1, 2023:
- Days between dates: (March 1 - January 1) = 59 days
- Pregnancy weeks: 59 days / 7 days per week ≈ 8.4 weeks
- Estimated due date: January 1, 2023 + 280 days = September 28, 2023
This would show you're in your 9th week of pregnancy (since weeks are typically counted from the first day of the last menstrual period).
Frequently asked questions
How accurate is this pregnancy week calculator?
This calculator provides an estimate based on standard pregnancy duration. Actual pregnancy lengths can vary, and medical professionals use ultrasound measurements for precise tracking.
Should I use LMP or conception date?
The calculator accepts both options. Most doctors use LMP for tracking, but some may use conception date if available.
What if my pregnancy is longer or shorter than 40 weeks?
This calculator uses the standard 40-week duration. If your pregnancy is significantly longer or shorter, consult with your healthcare provider.