Pregnancy Week Calculator
Use this calculator to estimate your current pregnancy week and estimated due date based on the first day of your last menstrual period (LMP).
Understanding Your Pregnancy Weeks
Pregnancy is a remarkable journey, typically lasting about 40 weeks from the first day of your last menstrual period (LMP). While conception usually occurs around two weeks after your LMP, medical professionals use the LMP as the starting point for consistency in tracking.
How Pregnancy Weeks Are Calculated
The most common method for calculating pregnancy duration is based on your Last Menstrual Period (LMP). This calculator uses that standard approach:
- First Day of LMP: You provide the date of the first day of your last menstrual period.
- Current Date: The calculator determines the number of days that have passed since your LMP.
- Weeks and Days: This total number of days is then converted into weeks and remaining days to give you your current pregnancy week.
- Estimated Due Date (EDD): Your EDD is typically calculated by adding 280 days (40 weeks) to your LMP date.
Why is the LMP Method Used?
It can be difficult to pinpoint the exact date of conception. The LMP provides a clear, consistent reference point that most women can recall. Even if you know your conception date, doctors often still use the LMP to align with standard medical charting and milestones.
Important Considerations
- Variations: While 40 weeks is the average, a full-term pregnancy can range from 37 to 42 weeks.
- Ultrasound Confirmation: Early ultrasounds can provide a more accurate estimated due date, especially if your menstrual cycles are irregular or you're unsure of your LMP. Your healthcare provider will use a combination of your LMP and ultrasound findings to give you the most precise due date.
- Not a Medical Diagnosis: This calculator provides an estimate for informational purposes only. Always consult with your doctor or healthcare provider for personalized medical advice, diagnosis, and treatment regarding your pregnancy.
Example Calculation:
Let's say your Last Menstrual Period (LMP) started on January 1, 2024. If today's date is April 15, 2024:
- Days from Jan 1 to Jan 31: 31 days
- Days in Feb (2024 is a leap year): 29 days
- Days in Mar: 31 days
- Days in Apr (up to 15th): 15 days
- Total days passed: 31 + 29 + 31 + 15 = 106 days
- Current Pregnancy Weeks: 106 days / 7 days/week = 15 weeks and 1 day.
- Estimated Due Date: January 1, 2024 + 280 days = October 8, 2024.
This calculator will perform these calculations instantly for you!
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function calculatePregnancyWeek() {
var lmpDateInput = document.getElementById("lastMenstrualPeriodDate").value;
var resultDiv = document.getElementById("pregnancyResult");
resultDiv.innerHTML = ""; // Clear previous results
if (!lmpDateInput) {
resultDiv.innerHTML = "Please enter the first day of your Last Menstrual Period.";
return;
}
var lmpDate = new Date(lmpDateInput);
var today = new Date();
// Set time to midnight for accurate day calculation
lmpDate.setHours(0, 0, 0, 0);
today.setHours(0, 0, 0, 0);
// Calculate difference in milliseconds
var timeDiff = today.getTime() – lmpDate.getTime();
// Convert to days
var daysDiff = Math.floor(timeDiff / (1000 * 3600 * 24));
if (daysDiff < 0) {
resultDiv.innerHTML = "LMP date cannot be in the future. Please select a valid date.";
return;
}
var currentWeeks = Math.floor(daysDiff / 7);
var remainingDays = daysDiff % 7;
// Calculate Estimated Due Date (EDD)
// EDD is typically LMP + 280 days (40 weeks)
var eddDate = new Date(lmpDate.getTime());
eddDate.setDate(lmpDate.getDate() + 280);
var options = { year: 'numeric', month: 'long', day: 'numeric' };
var formattedEdd = eddDate.toLocaleDateString('en-US', options);
var weeksUntilFullTerm = Math.max(0, 40 – currentWeeks);
var daysUntilFullTerm = Math.max(0, (40 * 7) – daysDiff);
resultDiv.innerHTML =
"
Current Pregnancy: " + currentWeeks + " weeks and " + remainingDays + " days" +
"
Estimated Due Date (EDD): " + formattedEdd + "" +
"
Weeks Remaining Until Full Term (40 weeks): " + weeksUntilFullTerm + " weeks and " + (daysUntilFullTerm % 7) + " days";
}