🤰 Pregnancy Weeks Calendar

Automatically calculates expected delivery date, current gestational week, and trimester by simply entering the date of last menstrual period. Displays weekly baby growth milestones and size comparisons.

Enter last menstrual period date

Growth Milestones

Usage and Tips

  • Enter the start date of your last menstrual period and click "Calculate
  • Expected delivery date is calculated at 280 days (40 weeks and 0 days) (Negele's approximation method)
  • Actual due date is based on physician's diagnosis. This tool is for reference only.
  • Milestones show the size of the baby at each week, compared to familiar objects

What is Pregnancy Calendar?

The Pregnancy Week Calculator automatically computes key pregnancy milestones from your last menstrual period (LMP). It calculates your expected due date, current gestational week, and which trimester you're in. The tool displays a visual calendar showing your pregnancy timeline, helping you track your progress and understand what to expect during each stage. It's a handy reference for pregnant individuals, partners, and healthcare providers.

How to Use

Enter the date of your last menstrual period in the input field. The calculator immediately displays your estimated due date (typically 280 days or 40 weeks from your LMP). It shows your current week of pregnancy and which trimester you're in. The tool provides a calendar view highlighting your pregnancy timeline from conception through delivery. Most versions allow you to adjust if you have an ultrasound-confirmed due date, which may differ slightly from LMP calculations. Bookmark the result to track progress throughout your pregnancy, and check back regularly to update your current week.

Use Cases

Pregnant individuals use this during their first prenatal visit to establish their due date. Partners and family members track pregnancy progress and plan for baby's arrival. Healthcare providers reference it to monitor gestational age during regular checkups. Expectant parents plan maternity leave, childcare, and nursery setup around the due date. Educators and employers use confirmed due dates for reasonable accommodation planning. The tool helps manage pregnancy-related decisions that depend on gestational age, such as prenatal testing schedules and delivery planning timelines.

Tips & Insights

LMP-based dating is accurate within a few days; ultrasound dating in the first trimester is more precise. Due dates are estimates—only about 5% of babies arrive exactly on their due date. Your trimester breakdown: first (weeks 1-13), second (weeks 14-27), third (weeks 28-40). Each trimester brings different physical changes and developmental milestones for the baby. Regular prenatal checkups are essential; the calculator is informational, not a replacement for medical guidance from your healthcare provider.

Frequently Asked Questions

How is the expected delivery date calculated?

Add 280 days (40 weeks) to the start of the last menstrual period (Negele's approximate method). The actual expected delivery date is determined by the doctor based on ultrasound examinations, etc., and should be used as a guide only.

What is a trimester?

The pregnancy period is divided into three segments. The first trimester (0-13 weeks) is the period of organogenesis, the second trimester (14-27 weeks) is the stable period, and the third trimester (28-40 weeks) is the period of preparation for delivery.

Is the baby's size accurate?

The sizes shown are general averages. Since there are individual differences, please check the exact developmental status at an obstetrician/gynecologist's checkup.

How accurate is the expected delivery date?

The calculation assumes a standard 280-day pregnancy (40 weeks) and is typically accurate within ±2 weeks for most pregnancies. Actual delivery naturally varies based on genetics, maternal health, and fetal development. Always confirm dates with your healthcare provider.

Can I track twins or multiple pregnancies?

The calculator is designed for single pregnancies. Twins and multiples typically deliver earlier (around 37 weeks for twins), so the standard 40-week calculation may not apply. Consult your doctor for personalized timeline information.

What if my menstrual cycle is irregular?

This calculator assumes a standard 28-day cycle. If your cycle is significantly longer (30+ days) or shorter (24 days or less), the estimated due date may be off by several days. Your healthcare provider can adjust dates using ultrasound measurements, which are more accurate.

Can I calculate from conception date instead of LMP?

No, the tool only accepts last menstrual period date. If you know conception date, add 14 days to estimate your LMP (conception typically occurs around day 14 of the cycle), then enter that date for better accuracy.

What important developments happen in each trimester?

The first trimester focuses on critical organ formation, the second on fetal growth and movement detection, and the third on final development and delivery preparation. Knowing your trimester helps you understand typical experiences and what healthcare providers monitor.

What should I do if my ultrasound dates don't match my LMP calculation?

Trust the ultrasound dates, as they are significantly more accurate than LMP calculations. Early pregnancy ultrasounds can determine age within ±3-5 days. Your healthcare provider will officially adjust your due date based on imaging results.