Enter your Last Menstrual Period (LMP) or your estimated conception date to find out your estimated due date (EDD).
Your Pregnancy Timeline
Estimated Due Date (EDD)–
Current Week of Pregnancy–
Weeks Until Due Date–
Understanding Your Pregnancy Timeline
The American Pregnancy Calculator helps estimate key dates in your pregnancy journey. The most common method for calculating these dates is based on your Last Menstrual Period (LMP). This method assumes a standard 28-day menstrual cycle where ovulation occurs around day 14.
How the Calculation Works (Based on LMP):
Estimated Due Date (EDD): The EDD is typically calculated using Naegele's Rule. This involves adding 7 days to the first day of your LMP and then subtracting 3 months, or adding 9 months and 7 days to the first day of your LMP. This results in an estimated 40-week gestation period from the start of your LMP.
Current Week of Pregnancy: This is calculated by determining the number of days or weeks that have passed since your LMP. For example, if today's date is 2 weeks and 3 days after your LMP, you are considered 2 weeks pregnant.
Weeks Until Due Date: This is the difference between your calculated EDD and the current date.
Using Conception Date:
If you know your estimated conception date (which typically occurs about two weeks after your LMP in a standard cycle), you can use this as an alternative input. The calculator will add approximately 38 weeks (266 days) to the conception date to estimate your due date. This method can be more accurate if your cycle length is irregular or if you know the exact date of conception.
Important Considerations:
This calculator provides an estimation. Pregnancies can vary, and due dates are averages. A full-term pregnancy is generally considered to be between 37 and 42 weeks.
Always consult with your healthcare provider for the most accurate dating of your pregnancy and personalized advice. Ultrasounds, especially those performed in the first trimester, are often considered the most accurate method for determining gestational age.
Factors like irregular cycles, early or late ovulation, and the exact moment of conception can affect the actual length of pregnancy.
Example:
If your LMP was on January 15, 2024:
Adding 7 days to January 15th gives January 22nd.
Adding 9 months to January 22nd brings you to October 22nd.
Adding 7 days to October 22nd gives you an estimated due date of October 29, 2024.
If today's date is February 10, 2024:
The pregnancy has progressed for approximately 3 weeks and 6 days since January 15, 2024. So, you are roughly 3 weeks pregnant.
The number of weeks until your due date would be approximately 38 weeks (40 weeks – 3 weeks).
function calculatePregnancyDates() {
var lmpDateInput = document.getElementById("lmpDate");
var conceptionDateInput = document.getElementById("conceptionDate");
var eddResultSpan = document.getElementById("eddResult");
var currentWeekResultSpan = document.getElementById("currentWeekResult");
var weeksUntilDueResultSpan = document.getElementById("weeksUntilDueResult");
var lmpDateStr = lmpDateInput.value;
var conceptionDateStr = conceptionDateInput.value;
var today = new Date();
today.setHours(0, 0, 0, 0); // Normalize today's date to midnight
var edd = null;
var pregnancyStartDate = null;
if (lmpDateStr) {
var lmpDate = new Date(lmpDateStr);
lmpDate.setHours(0, 0, 0, 0);
if (isNaN(lmpDate.getTime())) {
alert("Please enter a valid Last Menstrual Period date.");
return;
}
pregnancyStartDate = lmpDate;
// Naegele's Rule: Add 1 year, 7 days, subtract 3 months
var eddByLMP = new Date(lmpDate);
eddByLMP.setDate(eddByLMP.getDate() + 7);
eddByLMP.setMonth(eddByLMP.getMonth() – 3);
edd = eddByLMP;
} else if (conceptionDateStr) {
var conceptionDate = new Date(conceptionDateStr);
conceptionDate.setHours(0, 0, 0, 0);
if (isNaN(conceptionDate.getTime())) {
alert("Please enter a valid Estimated Conception date.");
return;
}
pregnancyStartDate = new Date(conceptionDate);
pregnancyStartDate.setDate(pregnancyStartDate.getDate() – 14); // Approximate LMP based on conception
// Standard gestation is 38 weeks from conception
var eddByConception = new Date(conceptionDate);
eddByConception.setDate(eddByConception.getDate() + (38 * 7)); // Add 38 weeks (266 days)
edd = eddByConception;
} else {
alert("Please enter either your Last Menstrual Period (LMP) or your Estimated Conception Date.");
return;
}
// Format EDD
if (edd) {
var options = { year: 'numeric', month: 'long', day: 'numeric' };
eddResultSpan.textContent = edd.toLocaleDateString(undefined, options);
} else {
eddResultSpan.textContent = "-";
}
// Calculate current week and weeks until due date
if (pregnancyStartDate && !isNaN(pregnancyStartDate.getTime())) {
var timeDiff = today.getTime() – pregnancyStartDate.getTime();
var daysDiff = Math.floor(timeDiff / (1000 * 60 * 60 * 24));
var weeksPregnancy = Math.floor(daysDiff / 7);
var remainingDaysInWeek = daysDiff % 7;
var currentWeekText = weeksPregnancy + " weeks and " + remainingDaysInWeek + " days";
currentWeekResultSpan.textContent = currentWeekText;
if (edd) {
var timeDiffToEdd = edd.getTime() – today.getTime();
var daysUntilDue = Math.ceil(timeDiffToEdd / (1000 * 60 * 60 * 24));
var weeksUntilDue = Math.floor(daysUntilDue / 7);
var remainingDaysUntilDue = daysUntilDue % 7;
var weeksUntilDueText = weeksUntilDue + " weeks and " + remainingDaysUntilDue + " days";
weeksUntilDueResultSpan.textContent = weeksUntilDueText;
} else {
weeksUntilDueResultSpan.textContent = "-";
}
} else {
currentWeekResultSpan.textContent = "-";
weeksUntilDueResultSpan.textContent = "-";
}
}