Determining how far along you are in pregnancy is crucial for tracking fetal development, scheduling prenatal appointments, and preparing for childbirth. The most common method for calculating gestational age is based on the Last Menstrual Period (LMP).
Gestational age is typically measured in weeks and days from the first day of your last menstrual period. A full-term pregnancy is considered to be 40 weeks (280 days) from the LMP.
Method 1: Based on Last Menstrual Period (LMP)
This calculator uses your reported LMP to estimate your due date and current gestational age. It assumes a standard 28-day cycle and ovulation occurring around day 14. The due date is generally calculated by adding 40 weeks (280 days) to the first day of your LMP.
Calculation:
Due Date: LMP + 40 weeks (280 days)
Current Gestational Age: The number of weeks and days that have passed since the LMP.
For example, if your LMP was January 1st, 2023:
Your estimated due date would be October 8th, 2023 (40 weeks later).
If today's date is March 15th, 2023, you are approximately 10 weeks and 4 days pregnant.
Method 2: Based on Current Gestational Age Inputs
If you know your current gestational age in weeks and days, you can use those inputs directly. This is often the case if you have had an early ultrasound that provided a more precise age.
This calculator can also provide an estimated due date if you input your LMP and your current gestational age.
Why is this important?
Knowing your gestational age helps you and your healthcare provider:
Monitor your baby's growth and development.
Understand which developmental milestones your baby is reaching.
Schedule important prenatal tests and ultrasounds at the appropriate times.
Prepare for labor and delivery based on your estimated due date.
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 calculatePregnancyStage() {
var lmpInput = document.getElementById("lastMenstrualPeriod");
var weeksInput = document.getElementById("gestationalAgeWeeks");
var daysInput = document.getElementById("gestationalAgeDays");
var resultDiv = document.getElementById("result");
var lmpDate = lmpInput.value;
var currentWeeks = parseInt(weeksInput.value);
var currentDays = parseInt(daysInput.value);
// Clear previous result
resultDiv.innerHTML = ";
resultDiv.classList.remove('show');
// Validate inputs
if (!lmpDate) {
resultDiv.innerHTML = "Please enter your Last Menstrual Period (LMP).";
resultDiv.classList.add('show');
return;
}
var now = new Date();
var lmp = new Date(lmpDate);
// Calculate difference in days from LMP
var timeDiff = now.getTime() – lmp.getTime();
var daysSinceLMP = Math.floor(timeDiff / (1000 * 60 * 60 * 24));
// Calculate total days from current weeks and days input
var totalCurrentDaysInput = (isNaN(currentWeeks) ? 0 : currentWeeks * 7) + (isNaN(currentDays) ? 0 : currentDays);
// Calculate estimated due date (40 weeks from LMP)
var edd = new Date(lmp.getTime());
edd.setDate(edd.getDate() + 280); // 40 weeks * 7 days/week
var eddString = edd.toDateString();
var calculatedWeeks;
var calculatedDays;
// Prioritize calculation based on LMP if dates are valid and current inputs are not provided or inconsistent
if (!isNaN(daysSinceLMP)) {
calculatedWeeks = Math.floor(daysSinceLMP / 7);
calculatedDays = daysSinceLMP % 7;
} else if (!isNaN(totalCurrentDaysInput) && totalCurrentDaysInput >= 0) {
// Use provided weeks and days if LMP calculation is not possible or if user specifically inputs age
calculatedWeeks = Math.floor(totalCurrentDaysInput / 7);
calculatedDays = totalCurrentDaysInput % 7;
// If weeks and days are provided, recalculate LMP and EDD for consistency
var calculatedLMP = new Date(now.getTime());
calculatedLMP.setDate(calculatedLMP.getDate() – totalCurrentDaysInput);
lmp = calculatedLMP; // Update lmp to be consistent with current age
edd = new Date(lmp.getTime());
edd.setDate(edd.getDate() + 280);
eddString = edd.toDateString();
} else {
resultDiv.innerHTML = "Invalid input. Please ensure dates and numbers are correct.";
resultDiv.classList.add('show');
return;
}
// Ensure days are not greater than 6
if (calculatedDays > 6) {
calculatedWeeks += Math.floor(calculatedDays / 7);
calculatedDays = calculatedDays % 7;
}
// Format the output string
var resultHTML = "Estimated Due Date: " + eddString + "";
resultHTML += "Current Gestational Age: " + calculatedWeeks + " weeks and " + calculatedDays + " days";
resultDiv.innerHTML = resultHTML;
resultDiv.classList.add('show');
}