How to Calculate How Far Along I Am in Pregnancy

Pregnancy Gestational Age and Due Date Calculator

Use this calculator to estimate your current gestational age (how many weeks and days pregnant you are) and your estimated due date (EDD) based on the first day of your last menstrual period (LMP).

function calculatePregnancy() { var lmpDateStr = document.getElementById("lmpDate").value; var currentDateStr = document.getElementById("currentDate").value; var resultDiv = document.getElementById("pregnancyResult"); resultDiv.innerHTML = ""; // Clear previous results if (!lmpDateStr) { resultDiv.innerHTML = "Please enter the first day of your Last Menstrual Period."; return; } var lmp = new Date(lmpDateStr + "T00:00:00"); // Add T00:00:00 to ensure UTC interpretation for consistency var today; if (currentDateStr) { today = new Date(currentDateStr + "T00:00:00"); } else { today = new Date(); today.setHours(0, 0, 0, 0); // Set to start of day for consistent calculation } if (isNaN(lmp.getTime())) { resultDiv.innerHTML = "Invalid LMP date. Please use a valid date format."; return; } if (isNaN(today.getTime())) { resultDiv.innerHTML = "Invalid current date. Please use a valid date format."; return; } if (lmp.getTime() > today.getTime()) { resultDiv.innerHTML = "The LMP date cannot be in the future relative to today's date."; return; } var diffTime = today.getTime() – lmp.getTime(); var diffDays = Math.floor(diffTime / (1000 * 60 * 60 * 24)); var weeks = Math.floor(diffDays / 7); var days = diffDays % 7; var edd = new Date(lmp.getTime() + (280 * 24 * 60 * 60 * 1000)); // 40 weeks = 280 days var eddFormatted = edd.toLocaleDateString('en-US', { year: 'numeric', month: 'long', day: 'numeric' }); var trimester = ""; if (weeks >= 0 && weeks = 13 && weeks = 28) { trimester = "Third Trimester"; } else { trimester = "Not yet in a recognized trimester (LMP is very recent)"; } var resultHTML = "

Your Pregnancy Details:

"; resultHTML += "Gestational Age: " + weeks + " weeks and " + days + " days"; resultHTML += "Estimated Due Date (EDD): " + eddFormatted + ""; resultHTML += "Current Trimester: " + trimester + ""; if (weeks > 42) { resultHTML += "Note: You are past the typical full-term pregnancy duration. Please consult your healthcare provider."; } else if (weeks < 0) { resultHTML = "The LMP date cannot be in the future relative to today's date."; } resultDiv.innerHTML = resultHTML; } // Set default value for currentDate to today's date document.addEventListener('DOMContentLoaded', function() { var today = new Date(); var dd = String(today.getDate()).padStart(2, '0'); var mm = String(today.getMonth() + 1).padStart(2, '0'); //January is 0! var yyyy = today.getFullYear(); document.getElementById('currentDate').value = yyyy + '-' + mm + '-' + dd; }); .pregnancy-calculator-container { font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif; background-color: #f9f9f9; border: 1px solid #e0e0e0; border-radius: 8px; padding: 25px; max-width: 600px; margin: 20px auto; box-shadow: 0 4px 12px rgba(0, 0, 0, 0.08); color: #333; } .pregnancy-calculator-container h2 { color: #4CAF50; text-align: center; margin-bottom: 20px; font-size: 1.8em; } .pregnancy-calculator-container p { line-height: 1.6; margin-bottom: 15px; } .calculator-form label { display: block; margin-bottom: 8px; font-weight: bold; color: #555; } .calculator-form input[type="date"] { width: calc(100% – 22px); padding: 10px; margin-bottom: 15px; border: 1px solid #ccc; border-radius: 5px; font-size: 1em; box-sizing: border-box; } .calculator-form button { background-color: #4CAF50; color: white; padding: 12px 20px; border: none; border-radius: 5px; cursor: pointer; font-size: 1.1em; width: 100%; transition: background-color 0.3s ease; } .calculator-form button:hover { background-color: #45a049; } .calculator-result { margin-top: 25px; padding: 20px; background-color: #e8f5e9; border: 1px solid #c8e6c9; border-radius: 8px; font-size: 1.1em; color: #2e7d32; } .calculator-result h3 { color: #2e7d32; margin-top: 0; margin-bottom: 15px; font-size: 1.4em; } .calculator-result p { margin-bottom: 10px; } .calculator-result p strong { color: #1b5e20; }

Understanding Pregnancy Dating

Calculating how far along you are in pregnancy is a fundamental step for expectant parents and healthcare providers. The most common method for dating a pregnancy is based on the first day of your Last Menstrual Period (LMP).

The LMP Method Explained

Pregnancy is typically considered to last about 40 weeks (or 280 days) from the first day of your LMP. This might seem a bit counterintuitive, as conception usually occurs about two weeks after your LMP. However, because it's often difficult to pinpoint the exact moment of conception, and menstrual cycles are a more reliable marker, medical professionals use the LMP as the starting point.

How the Calculator Works

Our calculator takes the first day of your LMP and the current date to determine:

• Gestational Age: This is the number of weeks and days you are currently pregnant, counted from your LMP.
• Estimated Due Date (EDD): This is the date 40 weeks (280 days) after your LMP, which is your baby's approximate arrival date. Keep in mind that only about 5% of babies are born exactly on their due date; most arrive within a week or two before or after.
• Current Trimester: Pregnancy is divided into three trimesters, each with its own developmental milestones and maternal changes:
  • First Trimester: Weeks 1-12
  • Second Trimester: Weeks 13-27
  • Third Trimester: Weeks 28 until birth

Why is Accurate Dating Important?

Knowing your gestational age and EDD is crucial for several reasons:

• Monitoring Fetal Development: It helps healthcare providers track your baby's growth and development against expected milestones.
• Scheduling Tests and Screenings: Many prenatal tests (like ultrasounds, genetic screenings) are time-sensitive and need to be performed within specific gestational windows.
• Planning for Delivery: Accurate dating helps in making informed decisions about labor and delivery, especially if there are concerns about preterm birth or post-term pregnancy.

Important Considerations

While the LMP method is widely used, it's most accurate for women with regular menstrual cycles. If your cycles are irregular, or if you're unsure of your LMP, your healthcare provider might use an early ultrasound to confirm or adjust your due date. Ultrasound measurements, especially those taken in the first trimester, can provide a very accurate gestational age.

Example Calculation:

Let's say your Last Menstrual Period (LMP) started on January 1, 2024, and today's date is April 15, 2024.

• The calculator would determine the number of days between January 1, 2024, and April 15, 2024.
• This difference is approximately 105 days.
• Dividing 105 days by 7 gives 15 weeks. So, you would be 15 weeks and 0 days pregnant.
• Your Estimated Due Date (EDD) would be 40 weeks (280 days) from January 1, 2024, which falls around October 8, 2024.
• At 15 weeks, you would be in your Second Trimester.

Always remember that this calculator provides an estimate. For precise dating and personalized medical advice, please consult with your doctor or midwife.