pregnancy calculator and calendar

How this pregnancy calculator works

This tool estimates pregnancy milestones using standard obstetric dating rules. Most clinics calculate pregnancy as a 40-week timeline starting from the first day of your last menstrual period, not from conception. That means when you are “4 weeks pregnant,” conception usually happened around 2 weeks earlier.

If you use the conception date method, the calculator adds 266 days (38 weeks) to estimate your due date. If you use the LMP method, it adds 280 days (40 weeks), with an adjustment for cycle length when entered.

How to use the calculator

Method 1: Last menstrual period (LMP)

• Enter the first day of your last period.
• Enter your average cycle length (default 28 days).
• Click Calculate to see due date and milestones.

Method 2: Conception date

• Select Conception date in the method dropdown.
• Enter the estimated conception date.
• Click Calculate to generate your results and calendar.

Understanding your results

After calculation, you will get:

• Estimated due date: Your projected 40-week endpoint.
• Gestational age today: Current week/day of pregnancy based on your dates.
• Conception estimate: Useful when dating is based on LMP.
• Trimester dates: Approximate start/end windows for each trimester.
• Full-term window: Typical delivery window between 37 and 42 weeks.

Pregnancy calendar by trimester

First trimester (weeks 1–13)

Major internal development starts quickly. Many people experience fatigue, nausea, breast tenderness, and mood changes. Prenatal vitamins with folic acid are especially important during this stage.

Second trimester (weeks 14–27)

Energy often improves, and early symptoms may ease. Anatomy scans are commonly performed around 18–22 weeks. You may begin to feel movement (“quickening”), usually around 16–22 weeks.

Third trimester (weeks 28–40)

Growth accelerates and prenatal visits may become more frequent. Planning for labor, delivery, feeding, sleep, and postpartum support becomes essential as you approach your due date.

Planning checklist for expecting parents

• Schedule regular prenatal visits and recommended screening tests.
• Track blood pressure, weight, symptoms, and fetal movement as advised.
• Build nutrition and hydration habits that are realistic and consistent.
• Create a birth plan draft and discuss preferences with your care team.
• Prepare support for postpartum recovery, meals, and sleep.
• Install an infant car seat and review safe sleep basics before delivery.

FAQ

How accurate is a due date calculator?

It is an estimate. Even with strong dating information, spontaneous labor can occur before or after the projected due date. Ultrasound and clinician assessment may refine dates.

What if my cycle is irregular?

LMP-based dating may be less accurate for irregular cycles. In that case, conception timing and early ultrasound can provide better estimates.

Can I use this for IVF pregnancies?

IVF pregnancies are usually dated from embryo transfer details. This tool is educational and may not match IVF-specific clinical calculations exactly.

Medical note: This calculator is for informational use only and is not a diagnosis or medical advice. Always confirm dates, test timing, and care decisions with your obstetrician, midwife, or qualified healthcare professional.