Calculate the estimated gestational age based on the Last Menstrual Period (LMP) or Ultrasound Scan Date.
Last Menstrual Period (LMP)
Ultrasound Scan Date
Understanding Gestational Age
Gestational age is a crucial metric in prenatal care, referring to the time elapsed since the first day of the woman's last menstrual period (LMP). It is the standard measure used by healthcare providers to track pregnancy progression, schedule prenatal tests, and estimate the due date. It is typically expressed in weeks and days.
Methods of Calculation
There are two primary methods to estimate gestational age:
Last Menstrual Period (LMP): This is the most common and oldest method. It assumes that ovulation occurs around day 14 of a 28-day cycle and conception follows shortly after. The gestational age is calculated by adding 40 weeks (280 days) from the first day of the LMP, or by calculating the number of days that have passed since the LMP.
Ultrasound Scan: Early pregnancy ultrasounds, particularly those performed between 7 and 12 weeks of gestation, are considered highly accurate for dating the pregnancy. They measure specific fetal biometry (like the crown-rump length – CRL) which correlates closely with gestational age. Ultrasound dating can be more precise than LMP dating, especially if the LMP is uncertain or menstrual cycles are irregular.
How the Calculator Works
Our Gestation Age Calculator utilizes the standard methodologies:
Using LMP: When you provide the start date of your Last Menstrual Period, the calculator determines the number of days elapsed since that date. This is then typically converted into weeks and days. For example, if 100 days have passed since your LMP, the calculator will determine the equivalent weeks and days (e.g., 14 weeks and 2 days). A common convention is to add 2 weeks to the LMP date to estimate ovulation, and then add 266 days (40 weeks total) to find the estimated due date. For gestational age, we simply calculate the duration from the LMP date.
Using Ultrasound Data: If you have had an early ultrasound, you can input the scan date and the estimated gestational age in weeks and days provided by your healthcare provider. The calculator will then calculate the number of days elapsed between the scan date and the estimated due date (40 weeks from LMP equivalent) or simply present the duration from the scan date if that's the primary input. For the purpose of this calculator, we use the provided weeks and days, assuming these were derived from an early, accurate ultrasound.
Why Gestational Age Matters
Accurate gestational age is vital for:
Monitoring fetal growth and development.
Scheduling important prenatal screenings and tests at optimal times.
Assessing whether the baby is full-term, preterm, or post-term at birth.
Making informed decisions about medical interventions if necessary.
Disclaimer: This calculator is for informational purposes only and should not replace professional medical advice. Always consult with your healthcare provider for accurate pregnancy dating and management.
function toggleInputs() {
var calculationType = document.getElementById("calculationType").value;
var lmpInputs = document.getElementById("lmpInputs");
var ultrasoundInputs = document.getElementById("ultrasoundInputs");
if (calculationType === "lmp") {
lmpInputs.style.display = "block";
ultrasoundInputs.style.display = "none";
} else {
lmpInputs.style.display = "none";
ultrasoundInputs.style.display = "block";
}
}
function calculateGestationAge() {
var calculationType = document.getElementById("calculationType").value;
var resultDiv = document.getElementById("result");
resultDiv.textContent = "; // Clear previous result
var today = new Date();
var gestationWeeks = 0;
var gestationDays = 0;
if (calculationType === "lmp") {
var lmpDateInput = document.getElementById("lmpDate");
var lmpDateValue = lmpDateInput.value;
if (!lmpDateValue) {
resultDiv.textContent = "Please enter your LMP date.";
return;
}
var lmpDate = new Date(lmpDateValue);
var timeDiff = today.getTime() – lmpDate.getTime();
var daysSinceLMP = Math.floor(timeDiff / (1000 * 60 * 60 * 24));
if (daysSinceLMP < 0) {
resultDiv.textContent = "LMP date cannot be in the future.";
return;
}
gestationWeeks = Math.floor(daysSinceLMP / 7);
gestationDays = daysSinceLMP % 7;
resultDiv.textContent = "Gestational Age: " + gestationWeeks + " weeks and " + gestationDays + " days";
} else { // Ultrasound method
var ultrasoundDateInput = document.getElementById("ultrasoundDate");
var ultrasoundAgeWeeksInput = document.getElementById("gestationalAgeWeeks");
var ultrasoundAgeDaysInput = document.getElementById("gestationalAgeDays");
var ultrasoundDateValue = ultrasoundDateInput.value;
var ultrasoundAgeWeeksValue = ultrasoundAgeWeeksInput.value;
var ultrasoundAgeDaysValue = ultrasoundAgeDaysInput.value;
if (!ultrasoundDateValue || !ultrasoundAgeWeeksValue || !ultrasoundAgeDaysValue) {
resultDiv.textContent = "Please enter all ultrasound details.";
return;
}
var ultrasoundDate = new Date(ultrasoundDateValue);
var weeks = parseInt(ultrasoundAgeWeeksValue, 10);
var days = parseInt(ultrasoundAgeDaysValue, 10);
if (isNaN(weeks) || isNaN(days) || weeks < 0 || days = 7) {
resultDiv.textContent = "Please enter valid weeks (>=0) and days (0-6).";
return;
}
gestationWeeks = weeks;
gestationDays = days;
// To calculate the EDD from ultrasound, we'd need a reference point.
// For this calculator, if ultrasound date and age are provided,
// we'll assume these are the primary inputs for the *current* estimated age.
// If the user wants to calculate EDD from ultrasound date, that's a different logic.
// Here, we display the provided estimated age.
resultDiv.textContent = "Estimated Gestational Age: " + gestationWeeks + " weeks and " + gestationDays + " days";
}
}
// Initialize input visibility on page load
window.onload = toggleInputs;