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Pregnancy Calculator

Calculate your due date, conception date, and current pregnancy week. Track fetal development milestones week by week. Enter your last period or conception date to get instant results.

How Due Date Is Calculated

This calculator uses Naegele's rule, the standard medical method for estimating due dates. It adds 280 days (40 weeks) to the first day of your last menstrual period (LMP).

Pregnancy weeks are counted from the LMP, not conception. This means at conception, you're already considered 2 weeks pregnant. The calculation assumes a 28-day menstrual cycle with ovulation on day 14.

First Trimester

Weeks 1-13. Foundation period with major organ development.

Second Trimester

Weeks 14-27. Growth period with movement and development.

Third Trimester

Weeks 28-40+. Preparation period for birth and maturation.

Fetal Development by Week

Your baby grows from a poppy seed to a full-term baby over 40 weeks. Each week brings new milestones — from the first heartbeat at week 4 to opening eyes at week 28. The calculator shows your current week with size comparison (fruit/vegetable), weight, length, and key developmental milestones based on your due date.

Important Note

This calculator provides estimates based on average cycles. Only about 5% of babies are born on their exact due date. Always consult your healthcare provider for accurate due date determination and prenatal care. Early ultrasound measurements provide more precise dating than LMP alone.

Frequently Asked Questions

How is the due date calculated?▾
The due date is calculated using Naegele's rule: add 280 days (40 weeks) to the first day of your last menstrual period (LMP). This assumes a 28-day cycle with ovulation on day 14. The calculation is shown instantly when you enter your LMP or conception date.
How accurate are due dates?▾
Only about 5% of babies are born on their exact due date. Most full-term births occur between 37 and 42 weeks. Due dates are estimates based on average cycle length. Your healthcare provider may adjust your due date based on early ultrasound measurements, which are more accurate than LMP-based calculations.
What is Naegele's rule?▾
Naegele's rule is a standard method for estimating due date: start with the first day of your last period, add one year, subtract three months, and add seven days. Alternatively, add 280 days to your LMP. This method was developed in the 1800s and remains the standard calculation method today.
Can I calculate from conception date?▾
Yes — switch to "From Conception" mode and enter the date you conceived. The calculator will estimate your due date by adding 266 days (38 weeks) to the conception date. Conception typically occurs 12-24 hours after ovulation, which is usually around day 14 of a 28-day menstrual cycle.
What week does each trimester start?▾
The first trimester covers weeks 1-13 (months 1-3), the second trimester covers weeks 14-27 (months 4-6), and the third trimester covers weeks 28-40+ (months 7-9). Each trimester brings different developmental milestones and changes for both mother and baby.
How do I know my current week?▾
Enter the first day of your last period. The calculator shows your current week and day. Pregnancy weeks are counted from the first day of your LMP, not from conception. For example, if you're 8 weeks pregnant, conception occurred about 6 weeks ago.
What if my cycle isn't 28 days?▾
Naegele's rule assumes a 28-day cycle, but many women have shorter or longer cycles. If your cycle is shorter than 28 days, your due date may be earlier; if longer, it may be later. Healthcare providers typically adjust due dates based on early ultrasound measurements for better accuracy.