Due Date Calculator — Find Your Estimated Due Date & Pregnancy Milestones

By sadiqbd · June 6, 2026

Your due date is one of the most important dates you'll ever calculate

When you find out you're pregnant, the first question almost everyone asks is: when is the baby due? The due date sets the entire framework for prenatal care — when to schedule appointments, when to expect certain milestones, and when to be ready. Getting it right matters.

A due date calculator gives you an estimated due date (EDD) based on your last menstrual period or conception date, along with week-by-week pregnancy milestones to help you track where you are.

How Due Dates Are Calculated

Naegele's Rule (most common method)

The standard clinical formula:

EDD = First day of last menstrual period + 280 days (40 weeks)

Equivalently: add 1 year, subtract 3 months, add 7 days.

Example: Last menstrual period (LMP) = March 1, 2024 EDD = March 1 + 280 days = December 5, 2024

This formula assumes:

A 28-day menstrual cycle
Ovulation on day 14 of the cycle
Fertilisation at ovulation

For cycles significantly longer or shorter than 28 days, the estimate may shift. The calculator adjusts for cycle length if you provide it.

From conception date

If you know the approximate date of conception (from fertility tracking or IVF):

EDD = Conception date + 266 days (38 weeks)

IVF pregnancies often use the egg retrieval date as the reference point.

From ultrasound

An early ultrasound (before 14 weeks) provides the most accurate gestational age estimate. The sonographer measures the crown-rump length and calculates gestational age. If this differs significantly from the LMP-based estimate, the ultrasound date takes precedence in clinical practice.

How to Use the Due Date Calculator on sadiqbd.com

Enter your last menstrual period start date — or select conception date if known.
Enter your average cycle length — defaults to 28 days; adjust if yours differs.
Read your estimated due date — plus the current gestational week if you're already pregnant.

The calculator also typically shows:

Estimated conception date
End of first trimester (week 13)
End of second trimester (week 27)
Current gestational week and day

Pregnancy Timeline Overview

Pregnancy is divided into three trimesters, each with its own characteristics and milestones:

First Trimester (Weeks 1–13)

Conception occurs around week 2 (day 14 of cycle in a 28-day cycle)
A pregnancy test typically turns positive around week 4–5
Embryo's major organ systems begin forming in weeks 5–10
First heartbeat detectable by ultrasound around week 6–7
Risk of miscarriage is highest in this trimester (10–20% of known pregnancies)
Morning sickness, fatigue, and breast tenderness are common
First prenatal appointment typically at week 8–10

Second Trimester (Weeks 14–27)

Often called the "easier" trimester — nausea usually eases
Baby's movements (quickening) felt around week 18–22 for first pregnancies
Anatomy scan ultrasound at week 18–22 checks for structural development
Sex determination possible from around week 16–20
Third trimester preparation begins toward the end

Third Trimester (Weeks 28–40)

Baby undergoes rapid weight gain — from about 1 kg at week 28 to 3–3.5 kg at term
Weekly prenatal visits from week 36 onward
Baby typically moves into head-down position by week 34–36
"Full term" defined as week 39–40; "early term" 37–38; "late term" 41; "post-term" 42+
Labour can begin anytime from week 37 (full term) onward

Important Date Milestones to Track

Milestone	Approximate Week
Positive pregnancy test	Week 4–5
First prenatal visit	Week 8–10
End of first trimester	Week 13
Anatomy scan	Week 18–22
Glucose screening test	Week 24–28
Third trimester begins	Week 28
Group B Strep test	Week 35–37
Full term	Week 39–40
Post-term (past due)	Week 42+

Your healthcare provider will schedule specific appointments; these are general reference points.

How Accurate Is the Estimated Due Date?

The EDD is an estimate — not a prediction. Only about 5% of babies are born on their exact due date. About 80% of babies are born within two weeks of the estimated date (between week 38 and week 42).

Factors that affect timing:

First pregnancies tend to run slightly longer than subsequent pregnancies
Genetic factors — the gestational length your mother experienced is somewhat predictive for you
Baby's sex — some research suggests boys are marginally more likely to arrive past the due date
Accuracy of the LMP date

An ultrasound before 14 weeks is the most accurate way to establish gestational age. If your ultrasound date and LMP-based date differ by more than a week, discuss with your provider which date to use as your official EDD.

Tips for Using the Due Date Calculator

Use the LMP date, not a guessed conception date. Unless you have precise conception date information (from temperature tracking, ovulation tests, or IVF), LMP gives a more reliable baseline than estimating backwards from when you think you conceived.

Adjust for cycle length. If your cycle is consistently 35 days rather than 28, your ovulation is later — and your EDD should shift accordingly by about 7 days. The calculator handles this adjustment when you enter your cycle length.

Track gestational weeks, not months. Pregnancy is conventionally measured in weeks, not months. "I'm 26 weeks" is more clinically precise than "I'm in my 6th month." Know your current week — prenatal care schedules, test timing, and developmental milestones are all referenced in weeks.

Discuss with your provider. A due date calculator is a useful planning tool, not a medical assessment. Your healthcare provider may adjust the EDD based on clinical examination or ultrasound findings.

Frequently Asked Questions

Can I go into labour before my due date? Yes. Labour can begin any time from week 37 onward and is considered full term from week 39. About 10% of births occur before week 37 (preterm).

What happens if I go past my due date? Most providers will monitor closely after week 40 and may recommend induction of labour by week 41–42 to reduce the small risk of placental insufficiency. Post-term pregnancy (past week 42) is associated with slightly higher risks and is typically managed with induction.

Is the 40-week timeline accurate for everyone? Naegele's Rule is a population average. Individual variation exists. Some women naturally have slightly longer or shorter gestations. Ultrasound-based dating is more accurate for individuals, especially when cycle lengths are irregular.

Does the due date change during pregnancy? It can — if an early ultrasound shows a gestational age significantly different from the LMP estimate, the provider may revise the EDD. Late ultrasounds are less accurate for dating and rarely change the official EDD.

Is the due date calculator free? Yes — completely free, no sign-up required.

The due date is where pregnancy planning starts — prenatal appointments, preparation timelines, and parental leave all anchor to it. Getting a clear estimate early helps everything that follows make more sense.

Try the Due Date Calculator free at sadiqbd.com — find your estimated due date and track your pregnancy milestones.