Gestational Calculator

Calculate your estimated due date (EDD) and gestational age quickly and free.

Calculate using last menstrual period (LMP)

Enter the first day of your last menstrual period to calculate the estimated due date and current gestational age.

Calculate using first ultrasound data

Enter the date of your first ultrasound and how many weeks and days pregnant you were at that time.

Calculate gestational age from estimated due date (EDD)

If you already know your estimated due date, enter it to find out your current gestational age.

How does gestational age calculation work?

Naegele's Rule

The estimated due date is calculated by adding 280 days (40 weeks) to the first day of the last menstrual period. This is the standard method used by obstetricians.

Early Ultrasound

First trimester ultrasound is the most accurate method for dating a pregnancy. The crown-rump length (CRL) measurement allows precise estimation of gestational age.

Important Notice

This calculator is an informational tool and does not replace medical evaluation. Always consult your obstetrician for proper pregnancy monitoring.

Frequently asked questions about the gestational calculator

Add 280 days (40 weeks) to the first day of your last menstrual period (LMP). This is Naegele's rule, used by most obstetricians. You can also calculate it using your first ultrasound data for a more precise result.

LMP stands for last menstrual period — the first day of your most recent period. It is used as the starting point to calculate gestational age and the estimated due date, since it can usually be identified even before the pregnancy is confirmed.

Enter the first day of your last menstrual period (LMP) into the gestational calculator and the result will show your current gestational age in weeks and days. If you have your first ultrasound date, use the By Ultrasound tab for an even more precise calculation.

The first-trimester ultrasound, especially between weeks 7 and 13, is the most accurate method to estimate gestational age, because it uses the baby's measurement (CRL). The LMP calculation is a good initial estimate, but may vary with irregular cycles.

It is the classic formula used to estimate the due date: add 280 days (or 40 weeks) to the first day of the last menstrual period and adjust according to the length of the menstrual cycle. It is the method behind the EDD calculator.

No. The calculator is an informational tool to estimate dates, but prenatal care with ultrasound exams is essential to monitor the baby's development. At Derm Imagem you can schedule your obstetric ultrasound with a specialist physician.

Important notice

This calculator is an educational tool and does not replace a medical consultation. Results are estimates based on published models and may not apply to your case. Never make decisions about your health or your pregnancy without advice from your doctor.

Reviewed by: Dr. Peterson Fernandes — CRM-MG 42452 · RQE 37814

Last reviewed: 11/3/2026

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