Gestational Age Calculator Calculate gestational age and estimated due date from the last menstrual period.

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Gestational Age Calculator

Calculate gestational age and estimated due date from the last menstrual period.

Enter LMP Date

Select the first day of your last menstrual period.

Set Cycle Length

Enter your average cycle length (default 28 days).

View Results

See gestational age, due date, trimester, and milestone tracking.

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What Is Gestational Age Calculator?

The Gestational Age Calculator determines the current gestational age of a pregnancy based on the first day of the last menstrual period (LMP). It shows the age in weeks and days (the standard medical notation), the estimated due date using Naegele's rule (LMP + 280 days, adjusted for cycle length), the current trimester, a progress bar through the pregnancy, the estimated conception date, and a milestone checklist showing key pregnancy events from first heartbeat through full term. The cycle length adjustment accounts for ovulation timing differences in women with shorter or longer cycles. This tool is intended for informational purposes and should not replace professional medical advice.

Why Use Gestational Age Calculator?

Standard medical gestational age calculation (weeks + days)
Naegele's rule due date with cycle length adjustment
Trimester identification and progress tracking
Key pregnancy milestone checklist
Estimated conception date calculation
Easy-to-use with clear visual indicators

Common Use Cases

Prenatal Care

Track gestational age between prenatal appointments for reference.

Due Date Estimation

Calculate the estimated due date based on last menstrual period.

Milestone Tracking

See which pregnancy milestones have been reached and which are upcoming.

Healthcare Planning

Plan medical appointments and screenings based on gestational age.

Personal Reference

Keep track of pregnancy progress with a simple, private tool.

Technical Guide

Gestational age is calculated as the number of days between the LMP date and today, expressed as complete weeks and remaining days. The estimated due date uses Naegele's rule: LMP + 280 days, with an adjustment for cycle length (adding the difference between the actual cycle length and 28 days). The trimester is determined by gestational weeks: first trimester (weeks 1-12), second trimester (weeks 13-26), third trimester (weeks 27-40). The conception estimate is approximately 14 days after LMP, adjusted for cycle length. The progress percentage is calculated as (totalDays / 280) × 100, capped at 100%. Milestones are predefined at standard gestational week thresholds.

Tips & Best Practices

1
Use the first day of your last period, not the last day
2
Adjust the cycle length if your average cycle is not 28 days
3
The due date is an estimate — only 5% of babies are born on their due date
4
This tool is for informational purposes only — consult your healthcare provider
5
The milestone checklist shows standard developmental events by week

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Frequently Asked Questions

Q What is gestational age?

Gestational age is measured from the first day of the last menstrual period (LMP). It's typically about 2 weeks more than the actual age of the embryo/fetus.

Q What is Naegele's rule?

Naegele's rule estimates the due date by adding 280 days (40 weeks) to the first day of the last menstrual period.

Q How does cycle length affect the due date?

Women with longer cycles ovulate later, so their due dates are adjusted later by the same number of days beyond 28.

Q Is this tool medically accurate?

The calculations use standard medical formulas, but this tool is for informational purposes only. Always consult your healthcare provider for medical advice.

Q What are the pregnancy trimesters?

First trimester: weeks 1-12. Second trimester: weeks 13-26. Third trimester: weeks 27-40.

About This Tool

Gestational Age Calculator is a free online tool by FreeToolkit.ai. All processing happens directly in your browser — your data never leaves your device. No registration or installation required.