Conception Date & Due Date Calculator
Use this calculator to estimate your conception date, last menstrual period (LMP), and estimated due date (EDD). You only need to provide one of the dates below, and the calculator will determine the others based on standard pregnancy timelines.
Understanding Pregnancy Dating
Pregnancy dating is a crucial aspect of prenatal care, helping healthcare providers monitor fetal development and plan for delivery. There are a few common ways to estimate pregnancy dates, primarily based on your Last Menstrual Period (LMP) or the estimated date of conception.
How Pregnancy is Dated
- Last Menstrual Period (LMP): The most common method, pregnancy is typically counted from the first day of your last menstrual period. A full-term pregnancy is considered to be 40 weeks (280 days) from the LMP. This method assumes a regular 28-day menstrual cycle with ovulation occurring around day 14.
- Conception Date: If you know your exact conception date (e.g., through IVF or precise tracking of ovulation), pregnancy is counted as 38 weeks (266 days) from this date. This is because conception usually happens about two weeks after the LMP.
- Estimated Due Date (EDD): This is the projected date your baby will be born, typically 40 weeks from your LMP or 38 weeks from conception.
The Relationship Between Dates
The calculator uses the following standard relationships:
- LMP to EDD: Add 280 days (40 weeks) to the LMP.
- LMP to Conception: Add 14 days (2 weeks) to the LMP.
- Conception to EDD: Add 266 days (38 weeks) to the Conception Date.
These relationships allow the calculator to determine any two dates if one is known.
Why is Knowing These Dates Important?
- Monitoring Fetal Growth: Accurate dating helps ensure the baby is growing at an expected rate.
- Scheduling Tests: Many prenatal screenings and tests are time-sensitive and need to be performed within specific gestational windows.
- Planning for Delivery: Knowing the EDD helps you and your healthcare team prepare for labor and delivery.
- Identifying Preterm or Post-term Births: Accurate dating is essential for diagnosing and managing pregnancies that go significantly before or after the due date.
Limitations and Accuracy
While this calculator provides a good estimate, it's important to remember:
- Irregular Cycles: If you have irregular menstrual cycles, dating based on LMP can be less accurate.
- Early Ultrasound: An early ultrasound (typically between 8-12 weeks) is often considered the most accurate method for dating a pregnancy, as it measures the fetal crown-rump length. Your healthcare provider will use this to confirm or adjust your estimated due date.
- Individual Variation: Not all pregnancies last exactly 40 weeks, and babies can be born healthy a few weeks before or after their due date.
How to Use the Calculator
- Choose Your Input: Select whether you want to enter your Last Menstrual Period (LMP) Date, your Estimated Due Date (EDD), or your Conception Date.
- Enter the Date: Use the date picker to input the known date. Entering a date in one field will automatically clear the others to ensure only one input is used for calculation.
- Click "Calculate Dates": The calculator will then display the estimated LMP, Conception Date, and EDD.
Examples:
Example 1: Calculating from LMP
If your Last Menstrual Period (LMP) started on January 1, 2024:
- Estimated Conception Date: January 15, 2024 (14 days after LMP)
- Estimated Due Date (EDD): October 8, 2024 (280 days after LMP)
Example 2: Calculating from EDD
If your Estimated Due Date (EDD) is October 15, 2024:
- Estimated Last Menstrual Period (LMP): January 8, 2024 (280 days before EDD)
- Estimated Conception Date: January 22, 2024 (266 days before EDD)
Example 3: Calculating from Conception Date
If your Conception Date was February 1, 2024:
- Estimated Last Menstrual Period (LMP): January 18, 2024 (14 days before Conception)
- Estimated Due Date (EDD): October 24, 2024 (266 days after Conception)
.conception-date-calculator-container {
font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
max-width: 700px;
margin: 20px auto;
padding: 25px;
background-color: #f9f9f9;
border-radius: 10px;
box-shadow: 0 4px 12px rgba(0, 0, 0, 0.1);
color: #333;
}
.conception-date-calculator-container h2 {
text-align: center;
color: #2c3e50;
margin-bottom: 25px;
font-size: 1.8em;
}
.conception-date-calculator-container h3 {
color: #34495e;
margin-top: 30px;
margin-bottom: 15px;
font-size: 1.4em;
}
.conception-date-calculator-container p {
line-height: 1.6;
margin-bottom: 15px;
}
.calculator-form .form-group {
margin-bottom: 20px;
}
.calculator-form label {
display: block;
margin-bottom: 8px;
font-weight: bold;
color: #555;
}
.calculator-form input[type="date"] {
width: calc(100% – 22px);
padding: 12px;
border: 1px solid #ccc;
border-radius: 6px;
font-size: 1em;
box-sizing: border-box;
transition: border-color 0.3s ease;
}
.calculator-form input[type="date"]:focus {
border-color: #007bff;
outline: none;
box-shadow: 0 0 5px rgba(0, 123, 255, 0.2);
}
.calculate-button {
display: block;
width: 100%;
padding: 14px 20px;
background-color: #28a745;
color: white;
border: none;
border-radius: 6px;
font-size: 1.1em;
font-weight: bold;
cursor: pointer;
transition: background-color 0.3s ease, transform 0.2s ease;
margin-top: 25px;
}
.calculate-button:hover {
background-color: #218838;
transform: translateY(-2px);
}
.calculator-result {
margin-top: 30px;
padding: 20px;
background-color: #e9f7ef;
border: 1px solid #d4edda;
border-radius: 8px;
font-size: 1.1em;
color: #155724;
}
.calculator-result h3 {
color: #155724;
margin-top: 0;
font-size: 1.3em;
}
.calculator-result p {
margin-bottom: 10px;
}
.calculator-result strong {
color: #0f3d1a;
}
.calculator-result em {
display: block;
margin-top: 15px;
font-size: 0.9em;
color: #6c757d;
}
.calculator-article ul {
list-style-type: disc;
margin-left: 20px;
margin-bottom: 15px;
}
.calculator-article ol {
list-style-type: decimal;
margin-left: 20px;
margin-bottom: 15px;
}
.calculator-article li {
margin-bottom: 8px;
line-height: 1.5;
}
.calculator-article strong {
color: #333;
}
function calculateDates() {
var lmpDateInput = document.getElementById('lmpDate').value;
var eddDateInput = document.getElementById('eddDate').value;
var conceptionDateInput = document.getElementById('conceptionDate').value;
var lmp, edd, conception;
var PREGNANCY_DURATION_LMP_DAYS = 280; // 40 weeks
var PREGNANCY_DURATION_CONCEPTION_DAYS = 266; // 38 weeks
var OVULATION_OFFSET_DAYS = 14; // LMP to Conception
var msPerDay = 24 * 60 * 60 * 1000;
if (lmpDateInput) {
lmp = new Date(lmpDateInput);
if (isNaN(lmp.getTime())) {
document.getElementById('result').innerHTML = "Please enter a valid Last Menstrual Period date.";
return;
}
edd = new Date(lmp.getTime() + (PREGNANCY_DURATION_LMP_DAYS * msPerDay));
conception = new Date(lmp.getTime() + (OVULATION_OFFSET_DAYS * msPerDay));
} else if (eddDateInput) {
edd = new Date(eddDateInput);
if (isNaN(edd.getTime())) {
document.getElementById('result').innerHTML = "Please enter a valid Estimated Due Date.";
return;
}
lmp = new Date(edd.getTime() – (PREGNANCY_DURATION_LMP_DAYS * msPerDay));
conception = new Date(edd.getTime() – (PREGNANCY_DURATION_CONCEPTION_DAYS * msPerDay));
} else if (conceptionDateInput) {
conception = new Date(conceptionDateInput);
if (isNaN(conception.getTime())) {
document.getElementById('result').innerHTML = "Please enter a valid Conception Date.";
return;
}
lmp = new Date(conception.getTime() – (OVULATION_OFFSET_DAYS * msPerDay));
edd = new Date(conception.getTime() + (PREGNANCY_DURATION_CONCEPTION_DAYS * msPerDay));
} else {
document.getElementById('result').innerHTML = "Please enter at least one date to calculate.";
return;
}
// Format dates for display
var options = { year: 'numeric', month: 'long', day: 'numeric' };
var formattedLMP = lmp.toLocaleDateString('en-US', options);
var formattedConception = conception.toLocaleDateString('en-US', options);
var formattedEDD = edd.toLocaleDateString('en-US', options);
var resultHTML = "
Calculated Pregnancy Dates:
";
resultHTML += "
Estimated Last Menstrual Period (LMP): " + formattedLMP + "";
resultHTML += "
Estimated Conception Date: " + formattedConception + "";
resultHTML += "
Estimated Due Date (EDD): " + formattedEDD + "";
resultHTML += "
Please note: These are estimates based on standard calculations. Your healthcare provider will confirm dates, often with an early ultrasound, which can provide a more precise due date.";
document.getElementById('result').innerHTML = resultHTML;
}