Due Date Calculator

Due Date Calculator — Free Online Tool Updated Mar 2026

What Is a Due Date Calculator?

A due date calculator is a simple tool that estimates when your baby may be born. It uses a known date, such as your last menstrual period, conception date, ultrasound date, or IVF transfer date. The result is called an estimated due date (EDD), and it helps you plan pregnancy care.

In daily life, this date helps you plan checkups, scans, leave from work, and home preparation. In medical care, it helps your provider track growth milestones and decide the right timing for tests. The date is an estimate, so it can change after new clinical data, especially in early pregnancy.

Many people search for terms like “pregnancy due date calculator,” “when is my due date,” and “how many weeks pregnant am I.” This tool answers those questions in one place with one clear result. If your cycle is not regular, the ultrasound method may give a better timeline than LMP alone.

If you are planning pregnancy, you may also use our Ovulation Calculator and Pregnancy Conception Calculator for a fuller view of timing.

How to Use This Calculator

Use these steps in order. Keep your dates ready before you start. This process usually takes less than 2 minutes.

1. Step 1: Choose method — Select LMP, conception, ultrasound, or IVF transfer based on the date you know.
2. Step 2: Enter your date — Add the exact day, month, and year for your chosen method.
3. Step 3: Add cycle length — If you selected LMP, enter your average cycle length if it is not 28 days.
4. Step 4: Check method details — For IVF, choose day-3 or day-5 transfer for better estimate quality.
5. Step 5: Run calculation — Click calculate to view estimated due date and current pregnancy week.
6. Step 6: Review timeline — Check trimester range and key care windows for planning appointments.
7. Step 7: Confirm with provider — Compare this estimate with your doctor or midwife after scans.

Due Date Formula

The most common formula is based on Naegele’s rule. It is easy to understand and widely used as a starting point.

Another way to write it:

For conception date, the tool usually adds 266 days. For IVF, the added days depend on transfer day. These formulas are useful for planning, but ultrasound can improve dating in many cases, especially when periods are irregular.

Types of Due Date Methods

Each method can be useful in a different situation. Choosing the right method may improve estimate quality.

• LMP method: Best when periods are regular and the first day of last period is known clearly.
• Conception date method: Useful when ovulation tracking is reliable and conception date is known.
• Ultrasound dating method: Often preferred for clinical dating in early pregnancy.
• IVF day-3 transfer method: Uses transfer date with day-3 embryo timing adjustment.
• IVF day-5 transfer method: Uses transfer date with blastocyst timing adjustment.
• Cycle-adjusted LMP method: Adds or subtracts days if your cycle is shorter or longer than 28 days.

Due Date Methods: Key Differences

If you want the shortest answer: ultrasound and IVF-based dates often guide final care decisions, while LMP gives an early estimate. The best method depends on what data you know and how regular your cycle is.

For body health context in pregnancy, you can also check our BMI Calculator and Pregnancy Weight Gain Calculator.

Quick Due Date Reference Table

This table is a quick snippet-style guide you can use to estimate due dates by method. Real care decisions should still follow your provider’s clinical guidance.

Due Date Care by Country

Core due date math is similar worldwide, but care pathways can differ. The summary below is educational and may change as guidelines update.

United States

In the US, many clinics begin with LMP and then review early ultrasound findings. A clear timeline helps schedule screening tests, diabetes checks, and late-pregnancy planning. Work leave and insurance paperwork also depend on your estimated window, so keep all dates documented.

US pregnancy care is often shared between OB-GYN teams, family doctors, and hospital systems. For many people, a due date is practical for planning childcare, support, and transport to hospital. Your provider may revise the date if scan findings and LMP are far apart.

United Kingdom

The NHS due date journey also starts with early estimate and then scan-based review. NHS public guidance highlights that pregnancy can naturally range from 37 to 42 weeks. Midwife-led care and scheduled visits are common in routine pregnancies.

Canada

Canadian care pathways usually combine history, physical exam, and scan data. Provinces may differ in exact workflow, but the same principle applies: use due date as a care planning anchor, not as a guaranteed birthday.

Australia

Australia also uses standard obstetric dating methods and scan support. Public and private pathways can differ in logistics, but due date remains central for checkups, tests, and labor planning conversations.

India

In India, care settings vary by city and region. LMP-based estimates are common where scan access is limited, and ultrasound helps refine dating where available. Timely checkups and record-keeping are especially important for safe planning.

Common Mistakes to Avoid

These mistakes are very common and can affect planning quality:

• Using period end date instead of start date: This can shift estimate by several days.
• Ignoring cycle length: If your cycle is 33 days, a fixed 28-day assumption may be off.
• Assuming one exact birthday: Real birth can happen before or after estimated date.
• Skipping scan comparison: Early scan may provide better medical dating context.
• Not updating records: Keep one final provider-confirmed date for forms and leave requests.
• Using random online values: Entering guessed dates can create avoidable stress and confusion.

Legal and Workplace Notes

Due date itself is not a legal advice issue, but it can affect maternity leave paperwork, insurance claims, and workplace planning. Rules vary by country, state, and employer contract. Use your provider-issued timeline when you submit official forms.

In many places, paid leave eligibility depends on policy dates and paperwork timing. If your due date changes after scan review, update HR and insurance records early. This may help avoid delays in benefits or claim processing.

Pregnancy Planning by Life Stage

Everyone’s health story is different. These are general planning ideas, not personal medical instructions.

20s

Focus on cycle tracking, nutrition, sleep, and first prenatal booking as soon as pregnancy is confirmed. A clear due date helps build a calm month-by-month plan.

30s

Many people in this stage balance job and family planning at the same time. Use your due date timeline early for leave planning, financial planning, and appointment scheduling.

40s

Clinical follow-up may be closer in some pregnancies, so date tracking becomes even more important. Keep scan reports and provider notes together for easy review.

50s and beyond (including donor/assisted pathways)

If pregnancy occurs through assisted reproduction, treatment dates and provider plans are key. Use IVF-aware calculation mode and confirm all timeline points with your care team.

Real-World Scenarios

These examples show how results can change with method and input quality.

Scenario 1: Regular 28-day cycle (LMP)

Scenario 2: Longer cycle (33 days)

Scenario 3: Known conception date

Scenario 4: IVF Day-5 transfer

Scenario 5: LMP and scan mismatch

Frequently Asked Questions

About This Calculator

Trusted Resources

• CDC Pregnancy (USA public health guidance)
• NIH NICHD Pregnancy Resources (USA research and education)
• NHS Due Date Calculator (UK public service guidance)
• NICE Antenatal Care Guidance (UK guideline source)
• WHO Antenatal Care Guideline (global care framework)

Disclaimer