👶 Gestational Age Calculator
Calculate your current gestational age in weeks and days from your last menstrual period (LMP) or estimated due date (EDD). Includes trimester progress, milestone timeline, and delivery classification.
What Is Gestational Age?
Gestational age is the standard way healthcare providers measure the duration of a pregnancy. It is calculated from the first day of your last menstrual period (LMP), not from the date of conception. This standard is used because the exact date of conception is rarely known, while the LMP is usually easier to recall.
Because ovulation typically occurs about two weeks after the LMP, gestational age is usually about 2 weeks ahead of the actual fetal age (the time since conception).
Key points about gestational age:
- Measured in weeks and days — for example, "12w3d" means 12 weeks and 3 days.
- Full term is defined as 39–40 weeks (ACOG definition).
- Normal range for delivery is 37–42 weeks.
- Estimated due date (EDD) = LMP + 280 days (40 weeks).
How Is Gestational Age Calculated?
Gestational age is calculated using Naegele's rule, which states:
EDD = LMP + 280 days
where 280 days = 40 weeks from the first day of the last menstrual period
To find gestational age at any given date:
- Gestational Age = Days since LMP (converted to weeks and days)
- For example, if 87 days have passed since your LMP: 87 ÷ 7 = 12 weeks and 3 days
If you know your estimated due date (EDD), the calculator reverses the process:
- LMP = EDD − 280 days
- Then gestational age is calculated from that derived LMP.
Trimester Definitions
Pregnancy is divided into three trimesters:
- First Trimester (Weeks 1–13): Major organ development, highest risk of miscarriage.
- Second Trimester (Weeks 14–27): Fetal growth accelerates, movement felt (quickening), anatomy scan performed.
- Third Trimester (Weeks 28–40+): Rapid weight gain, lung maturation, preparation for delivery.
Delivery Classification
The timing of delivery is classified by gestational age:
- Extremely Preterm (< 28 weeks): Highest risk of complications.
- Very Preterm (28–31 weeks): Requires intensive neonatal care.
- Moderate Preterm (32–33 weeks): Common in twin pregnancies.
- Late Preterm (34–36 weeks): Near-term but still at risk.
- Early Term (37–38 weeks): Slightly elevated risk vs. full term.
- Full Term (39–40 weeks): Optimal delivery window.
- Late Term (41 weeks): Increased monitoring recommended.
- Post Term (42+ weeks): Higher risk of complications.
Why Use This Calculator?
- Instant results: Get your gestational age in weeks and days, plus due date.
- Trimester tracking: See which trimester you're in with a visual progress bar.
- Milestone timeline: Track key pregnancy milestones and upcoming tests.
- Delivery classification: Understand your delivery timing category.
- Free & private: No registration, no data storage — all calculations are done in your browser.
❓ Gestational Age Calculator FAQ
What is gestational age?
Gestational age is the age of a pregnancy measured from the first day of the last menstrual period (LMP). It is the standard way healthcare providers date pregnancies.
How is gestational age different from fetal age?
Gestational age is measured from the LMP, while fetal age (or embryonic age) is measured from conception. Gestational age is typically about 2 weeks ahead of fetal age.
How is the due date calculated?
The estimated due date (EDD) is calculated using Naegele's rule: EDD = LMP + 280 days (40 weeks). This assumes a regular 28-day menstrual cycle.
What is full term?
Full term is defined by ACOG as 39–40 weeks of gestation. The broader normal range for delivery is 37–42 weeks.
What are the trimesters?
First trimester: Weeks 1–13. Second trimester: Weeks 14–27. Third trimester: Weeks 28–40+.
What if my cycle is not 28 days?
If your cycle is longer or shorter than 28 days, your due date may need adjustment. Your healthcare provider can use an early ultrasound to establish a more accurate due date.
What is the viability threshold?
Viability — the point at which a fetus can potentially survive outside the womb — is generally considered to be around 24 weeks of gestation, though this varies by hospital and country.
How accurate is this calculator?
This calculator uses Naegele's rule and standard gestational age definitions. However, every pregnancy is unique. An early ultrasound (before 14 weeks) is the most accurate way to date a pregnancy. Always consult your healthcare provider.
Can I use this calculator for IVF pregnancy?
IVF pregnancies are dated differently — from the embryo transfer date, not the LMP. Your fertility clinic will provide a specific due date. This calculator is best for natural pregnancies.
Is this calculator free?
Yes, this calculator is completely free to use. No registration or personal data storage is required.