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Pregnancy Week Calculator

Calculate current gestational age and due date from last menstrual period or embryo transfer date

Gestational age is counted from conception; due date = conception + 266 days (38 weeks)

How does this calculator work?

  1. 1 Choose your dating method (last period or transfer date)
  2. 2 Enter the reference date
  3. 3 If using a transfer date, also select the embryo type
  4. 4 See your current weeks, progress through pregnancy, and due date

How Are Pregnancy Weeks Counted?

Gestational age = (today − LMP or estimated conception date) ÷ 7. A pregnancy spans 280 days (40 weeks) across three trimesters: first (1–12), second (13–27), and third (28–40).

The first trimester (1–12) is when organs form — take folic acid and avoid harmful substances. The second (13–27) brings rapid growth and routine prenatal checks. In the third (28–40) the baby matures and you prepare for delivery.

Counting weeks after IVF: Day 3 transfer date − 17 days, Day 5 − 19 days, Day 6 − 20 days gives the estimated conception date; count from there.

A due date is an estimate — actual delivery can fall within 2 weeks either side, and only about 5% arrive on the day. After week 37 labor can begin anytime, so have your plans ready.

How Are Pregnancy Weeks Calculated?

Pregnancy spans 280 days (40 weeks) in three stages: first trimester (weeks 1–12), second trimester (13–27), and third trimester (28–40).

Gestational age = (today − reference date) ÷ 7

What Should I Know in Each Trimester?

  • • The first trimester is critical for organ formation — keep up with folic acid
  • • The second trimester is a period of rapid growth — focus on balanced nutrition
  • • In the third trimester, prepare for delivery and learn the signs of labor
This calculator is for reference only and does not replace professional medical advice. Please consult your doctor for personalized guidance.

Frequently Asked Questions

When do pregnancy weeks start counting?
From the first day of your last period, even though conception happens about 2 weeks later. This is the universal medical standard.
What should I watch in the third trimester?
Monitor fetal movement, manage weight gain, pack your hospital bag, and learn the signs of labor: spotting, water breaking, and regular contractions.
How do I count weeks after an IVF transfer?
Subtract 17/19/20 days from your Day 3/5/6 transfer date to get the estimated conception date, then count weeks from there.
What happens at each stage of pregnancy?
Organs form in the first trimester (1–12), rapid growth happens in the second (13–27), and maturation completes in the third (28–40).

References

  • [1] ACOG confirms gestational age is counted from the first day of the last menstrual period — the international standard — ACOG - Pregnancy Dating
  • [2] The WHO divides pregnancy into three trimesters: first (weeks 1–12), second (weeks 13–27), and third (weeks 28–40) — WHO - Pregnancy Trimesters

Related calculators

Natural Pregnancy Due Date Calculator
Estimate your due date from last menstrual period (LMP), suitable for natural conception and IUI
IVF Due Date Calculator
Calculate your due date precisely from embryo transfer or egg retrieval date, supporting Day 3, Day 5, Day 6 blastocyst transfer

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