age of gestation calculator

What is gestational age?

Gestational age is the length of pregnancy measured in weeks and days, starting from the first day of the last menstrual period (LMP), not from conception. This standard dating method is used in prenatal care because the exact conception date is often unknown.

In most clinical settings, a full-term pregnancy is considered around 40 weeks (280 days) from LMP. That timeline helps providers schedule tests, monitor fetal growth, and plan prenatal milestones.

How this age of gestation calculator works

This calculator supports three methods so you can estimate gestational age from the data you have:

• From LMP: Uses the first day of your last menstrual period and optionally adjusts for cycle length.
• From due date: Works backward from an estimated due date.
• From conception date: Adds 14 days to conception to align with obstetric dating standards.

Once calculated, the tool shows your current pregnancy age, trimester, estimated due date, and how many days remain until due date (or days past due date).

Step-by-step instructions

1) Choose your method

Select the method that best matches your available information. If you know your LMP, that is usually the standard starting point.

2) Enter your date(s)

Provide the required date for your chosen method. If using LMP, you can also enter your average cycle length to get an adjusted estimate.

3) Set reference date

The reference date defaults to today, but you can choose any date to calculate gestational age at a past or future point in time.

4) Click calculate

The result will display pregnancy age in weeks and days, trimester, estimated due date, and additional timeline details.

Understanding the results

• Gestational age: Displayed as weeks + days (example: 23 weeks 4 days).
• Trimester: 1st (0-13w6d), 2nd (14w0d-27w6d), 3rd (28w0d+).
• Estimated due date (EDD): Approximate date of 40 weeks gestation.
• Progress: Percent of the standard 280-day pregnancy completed.

Important notes and limitations

All gestational calculators provide estimates. Real pregnancies vary naturally. Ovulation timing, implantation timing, and menstrual irregularity can shift dating.

For clinical decision-making, ultrasound and professional prenatal assessment are essential, especially in early pregnancy when dating accuracy matters most.

When to contact a healthcare professional

Use this calculator for planning and understanding, but seek medical guidance if you have:

• Uncertain or irregular cycles
• Bleeding, pain, or concerning symptoms
• Large differences between calculator estimate and ultrasound dating
• Questions about due date changes or prenatal test timing

Quick FAQ

Why does gestational age start before conception?

Because obstetric dating traditionally begins at LMP, which occurs about two weeks before ovulation in a typical 28-day cycle.

Can due dates change?

Yes. Early ultrasound can refine dating and may update the estimated due date based on fetal measurements.

Is 40 weeks exact?

No. It is a benchmark. Birth commonly occurs within a range around the due date.

Disclaimer: This tool is for educational use and is not a medical diagnosis. Always follow your obstetric clinician's guidance.