How accurate is a due date calculator?

It provides an estimate based on standard dating rules. Real delivery dates can vary, so the result is best used as a planning guide.

What is the best date to use: LMP, conception, or ultrasound?

If you know your LMP clearly, it's a common starting point. If your cycles are irregular or dates are uncertain, an early ultrasound estimate may be more helpful.

What if I don't remember the first day of my last period?

Use your best estimate, or choose a different method like conception date or ultrasound dating if available.

Can irregular periods affect the due date estimate?

Yes. Irregular cycles can make LMP-based dating less reliable. An early ultrasound may give a clearer estimate.

Why does the calculator ask for cycle length?

Cycle length can shift when ovulation likely happened. A longer or shorter cycle may change the estimated due date by a few days.

Is gestational age counted from conception?

No. Gestational age is usually counted from LMP. Conception is typically about two weeks after LMP in a 28-day cycle.

Can my due date change after an ultrasound?

It can. If early ultrasound measurements suggest a different timeline than LMP, a provider may update the due date.

What does EDD mean in pregnancy?

EDD stands for Estimated Due Date—the predicted date your pregnancy reaches about 40 weeks (when dated from LMP).

How do I calculate my due date if I did IVF?

IVF timing is often known more precisely. Many people use the embryo transfer date and the embryo's age at transfer to estimate the due date. Your clinic may provide an official date.

What if my due date is near the end of a month—could it be next month instead?

Yes. Due dates are based on day counts, not months, so it's normal for the estimate to fall on either side of a month boundary.

Does the due date predict the baby's exact birthday?

No. It's a best estimate. It helps track pregnancy progress, appointments, and milestones rather than predicting an exact delivery day.

Due Date Calculator: Estimate Your Baby's Arrival Date

A due date is an estimate of when your baby may arrive. This calculator helps you find that date using common medical dating methods, like the first day of your last menstrual period (LMP), your conception date, or an early ultrasound estimate. It's useful for anyone who is pregnant or trying to understand their pregnancy timeline. You'll get an expected due date and a clear view of how far along you are (or will be), so you can plan appointments, track milestones, and feel more prepared.

How to Use This Calculator

Choose the method you want to use:
- Last menstrual period (LMP)
- Conception date (if you know it)
- Ultrasound-based dating (gestational age on a scan date)
Enter the required date(s) for your chosen method.
If the calculator asks, enter your average cycle length (only if it differs from 28 days).
Click calculate to see your estimated due date.
Review the results, including pregnancy week/day and time remaining (if shown).

What This Calculator Measures

This calculator estimates your pregnancy due date, which is the expected end of pregnancy based on standard dating rules.

Key terms (plain and simple):

Due date (EDD): "Estimated Due Date," the best estimate of when labor may start.
LMP: The first day of your Last Menstrual Period. Many providers date pregnancy from this day.
Gestational age: How far along the pregnancy is, measured in weeks and days from LMP (not from conception).
Conception date: The approximate day fertilization happened. This is often harder to know exactly.

Formula or Logic

Most due date estimates start from one of two timelines:

From LMP: Pregnancy is commonly dated as 40 weeks (280 days) from the first day of your last period.
From conception: Conception typically happens about 2 weeks after LMP in a 28-day cycle. So, from conception, the estimate is about 38 weeks (266 days).

If your cycle is longer or shorter than 28 days, some calculators adjust the due date by a few days. Early ultrasounds can also estimate gestational age based on fetal measurements, which may shift the due date.

Example Calculations

Example 1: Using LMP (standard cycle)

Input: LMP = March 1, 2026
Output: Estimated due date ≈ December 6, 2026 (about 280 days later)

Example 2: Using conception date

Input: Conception date = April 10, 2026
Output: Estimated due date ≈ January 1, 2027 (about 266 days later)

Example 3: Using ultrasound dating

Input: Ultrasound date = May 20, 2026; Gestational age on scan = 10 weeks 0 days
Output: Estimated due date ≈ December 16, 2026 (40 weeks from the adjusted start point)

Understanding Your Results

Your result is an estimate, not a guarantee. It's a target date used for planning care and tracking pregnancy milestones.

What the numbers mean:

Estimated due date: The expected date at around 40 weeks of pregnancy (when dated from LMP).
Weeks and days pregnant: A timeline measure used in prenatal care (example: 18 weeks 3 days).
Time remaining: How many weeks/days are left until the estimated due date (if the tool displays it).

Different methods can give slightly different due dates. Healthcare providers often rely on LMP unless an early ultrasound suggests a better estimate.

Common Mistakes to Avoid

Entering the last day of your period instead of the first day (for LMP).
Using an estimated "period week" rather than the exact date.
Confusing gestational age (from LMP) with fetal age (from conception).
Forgetting to adjust for an unusual cycle length if the calculator asks.
Using a late ultrasound date for dating (early scans are typically more consistent for estimating timing).
Assuming the due date is an exact delivery date.
Mixing methods (example: LMP date plus ultrasound weeks) in the same calculation.

A due date is a helpful estimate that gives you a clear pregnancy timeline and a planning point for care and milestones. Use the method that best matches what you know—LMP, conception date, or ultrasound dating. Try the calculator above to see your results.

Frequently Asked Questions

Common questions about the Due Date Calculator are answered below.

Due Date Calculator