How accurate is a due date calculator?

LMP-based calculations are accurate within 5–7 days for women with regular 28-day cycles. A first-trimester ultrasound (weeks 6–13) is more accurate because it measures the baby's crown-rump length. Only about 5% of babies are born exactly on their due date — most arrive within the 37–42 week birth window.

What is an IVF due date calculation?

For IVF with a Day 5 blastocyst transfer, add 261 days (266 − 5) to the transfer date. For a Day 3 embryo transfer, add 263 days. The fertilisation date is used as the conception reference point.

What prenatal tests should I do in India?

Key tests in India include: First trimester NT scan (weeks 11–13), Double Marker test (weeks 11–13), Anomaly scan (week 20), Glucose Tolerance Test (week 24–28), and Group B Strep test (week 35–37). PMSMA (Pradhan Mantri Surakshit Matritva Abhiyan) provides free ANC services on the 9th of every month at government health facilities.

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Home›Health›Pregnancy Calculator

Pregnancy Due Date Calculator

Due date · Weeks pregnant · Baby size · Trimester progress · 40-week milestone table · Indian ANC schedule

Calculation Method

First Day of Last Menstrual Period (DD/MM/YYYY)

e.g. 01/05/2026 — enter the first day of your last period

Average Cycle Length (days) — optional

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Pregnancy Due Date Calculator – Week by Week, Baby Size & Milestones

SuccessMate's free pregnancy calculator supports four input methods: Last Menstrual Period (LMP), conception date, ultrasound gestational age, and IVF transfer date — covering every situation from natural conception to assisted reproduction. Whether you are newly pregnant in India, the USA, the United Kingdom, Canada, Australia, Germany or the UAE, you get your estimated due date, current pregnancy week, trimester status and a full 40-week milestone timeline instantly and without any login.

Naegele's Rule — The Standard Method

The most widely used method is Naegele's Rule: add 280 days (40 weeks) to the first day of your Last Menstrual Period. Alternatively, add one year, subtract three months and add seven days. For a 28-day cycle this is very accurate. For irregular cycles, an early ultrasound between weeks 6–13 provides the most precise dating by measuring the baby's crown-rump length (CRL).

Baby Size by Week — A Fruit-Size Guide

The calculator shows what fruit your baby's size is comparable to each week — from a poppy seed at week 4 to a watermelon at week 40. This helps parents visualise growth milestones and is one of the most shared features in pregnancy tracker apps like Flo, BabyCenter and What to Expect.

Indian Antenatal Care Schedule & PMSMA

The tool includes an India-specific ANC (Antenatal Care) schedule covering all recommended visits, tests and vaccinations under the national maternal health programme. PMSMA (Pradhan Mantri Surakshit Matritva Abhiyan) provides free comprehensive ANC checkups on the 9th of every month at government health facilities — an important resource for pregnant women across India.

❓ Frequently Asked Questions

How is a due date calculated? ▾

The standard method is Naegele's Rule: add 280 days (40 weeks) to the first day of your Last Menstrual Period. If you know your conception date, add 266 days. For IVF, add 266 days minus the embryo age at transfer. An ultrasound in weeks 6–13 gives the most accurate dating.

How accurate is the due date? ▾

LMP-based calculations are accurate within 5–7 days for regular 28-day cycles. First-trimester ultrasounds are more precise. Only about 5% of babies are born on the exact due date — most arrive within the natural birth window of 37–42 weeks.

What are the three trimesters? ▾

First trimester: weeks 1–13. Second trimester: weeks 14–26. Third trimester: weeks 27–40. The first trimester covers organ formation; the second, rapid growth and movement; the third, brain maturation, weight gain and preparation for birth.

How is an IVF due date calculated? ▾

For a Day 5 blastocyst transfer, add 261 days (266 − 5) to the transfer date. For a Day 3 transfer, add 263 days. For Day 6, add 260 days. IVF dates are generally the most accurate since conception timing is precisely known.

What prenatal tests should I have in India? ▾

Key tests include: NT scan + Double Marker (weeks 11–13), anomaly scan (week 20), Glucose Tolerance Test (weeks 24–28), and Group B Strep test (weeks 35–37). PMSMA provides free ANC on the 9th of every month at government facilities. Your doctor will recommend additional tests based on your individual risk factors.