estimated gestational age calculator

What is estimated gestational age?

Estimated gestational age is the length of pregnancy measured in weeks and days. In obstetrics, gestational age usually begins on the first day of the last menstrual period (LMP), not the day of conception. That means gestational age is commonly about two weeks ahead of fetal age.

This calculator gives a practical estimate you can use for planning appointments, understanding trimester timing, and tracking milestones. It is especially useful when you want a quick answer without manually counting days on a calendar.

How this calculator works

1) From LMP (most common method)

If you enter an LMP date, the calculator counts days from that date to your selected “as of” date. It also allows cycle-length adjustment. For cycles longer or shorter than 28 days, ovulation tends to shift, and this affects the estimate.

2) From estimated due date (EDD)

If you already have a due date from your clinician, the calculator works backward from a standard 280-day pregnancy length to estimate current gestational age.

3) From conception date

If conception is known, the calculator adds approximately 14 days to convert fetal age to gestational age. This aligns with standard obstetric dating conventions.

Understanding your results

• Gestational age: Displayed as weeks + days.
• Estimated due date: Based on your selected method.
• Trimester: First, second, or third trimester based on gestational age.
• Days pregnant / days remaining: Helpful for timeline planning.

Why your due date can change

It is common for due dates to be revised, especially after first-trimester ultrasound. Early ultrasound can provide more accurate dating than LMP alone, particularly when cycles are irregular or LMP is uncertain.

If your app, your memory of dates, and your ultrasound estimate differ, follow the date recommended by your prenatal care provider.

Tips for better accuracy

• Use the exact first day of your last period if known.
• Enter your typical cycle length, not an unusual outlier cycle.
• Use the EDD provided by your clinician when available.
• Recalculate using a specific “as of” date for future planning.

Important note

This calculator is intended for informational purposes only. It does not diagnose pregnancy complications, estimate labor timing with certainty, or replace prenatal care. If you have bleeding, severe pain, reduced fetal movement later in pregnancy, or any urgent concern, contact a healthcare professional promptly.