How to Calculate How Far Along Pregnant You Are

Pregnancy Week & Due Date Calculator

Enter the first day of your last menstrual period (LMP) to estimate your pregnancy week and due date.

Your Pregnancy Details:

function calculatePregnancy() { var lmpDateInput = document.getElementById('lmpDate').value; var resultDiv = document.getElementById('pregnancyResult'); var weeksPregnantElem = document.getElementById('weeksPregnant'); var estimatedDueDateElem = document.getElementById('estimatedDueDate'); var currentTrimesterElem = document.getElementById('currentTrimester'); var conceptionDateElem = document.getElementById('conceptionDate'); weeksPregnantElem.innerHTML = "; estimatedDueDateElem.innerHTML = "; currentTrimesterElem.innerHTML = "; conceptionDateElem.innerHTML = "; if (!lmpDateInput) { weeksPregnantElem.innerHTML = 'Please enter the first day of your Last Menstrual Period.'; return; } var lmpDate = new Date(lmpDateInput); var currentDate = new Date(); // Set time to midnight for accurate day calculation lmpDate.setHours(0, 0, 0, 0); currentDate.setHours(0, 0, 0, 0); if (lmpDate > currentDate) { weeksPregnantElem.innerHTML = 'LMP date cannot be in the future. Please enter a valid date.'; return; } var timeDiff = currentDate.getTime() – lmpDate.getTime(); var daysPregnant = Math.floor(timeDiff / (1000 * 60 * 60 * 24)); if (daysPregnant < 0) { // Should not happen with the above check, but good for robustness weeksPregnantElem.innerHTML = 'An error occurred. Please check your date input.'; return; } var weeks = Math.floor(daysPregnant / 7); var days = daysPregnant % 7; weeksPregnantElem.innerHTML = 'Weeks Pregnant: ' + weeks + ' weeks and ' + days + ' days'; // Calculate Estimated Due Date (EDD) – Naegele's Rule: LMP + 280 days (40 weeks) var eddDate = new Date(lmpDate.getTime()); eddDate.setDate(lmpDate.getDate() + 280); estimatedDueDateElem.innerHTML = 'Estimated Due Date (EDD): ' + eddDate.toLocaleDateString('en-US', { weekday: 'long', year: 'numeric', month: 'long', day: 'numeric' }); // Calculate Estimated Conception Date (LMP + 14 days) var conceptionDate = new Date(lmpDate.getTime()); conceptionDate.setDate(lmpDate.getDate() + 14); conceptionDateElem.innerHTML = 'Estimated Conception Date: ' + conceptionDate.toLocaleDateString('en-US', { year: 'numeric', month: 'long', day: 'numeric' }); // Determine Trimester var trimester = "; if (weeks >= 0 && weeks = 14 && weeks = 28) { trimester = 'Third Trimester'; } else { trimester = 'Not yet pregnant (or date too early)'; } currentTrimesterElem.innerHTML = 'Current Trimester: ' + trimester; if (weeks > 42) { weeksPregnantElem.innerHTML += 'This calculation suggests you are past your due date. Please consult your healthcare provider.'; } }

Understanding Your Pregnancy Weeks and Due Date

Calculating how far along you are in your pregnancy is one of the first and most exciting steps after a positive test. While only a healthcare professional can provide a definitive assessment, this calculator uses a widely accepted method to give you a good estimate.

The Last Menstrual Period (LMP) Method

The most common way to estimate pregnancy duration and a due date is by using the first day of your Last Menstrual Period (LMP). This method, often referred to as Naegele's Rule, works on the assumption that:

• Pregnancy lasts approximately 40 weeks (280 days) from the first day of your LMP.
• Ovulation and conception typically occur around two weeks after your LMP. This means that by the time you conceive, you are already considered "two weeks pregnant."

This calculator takes your LMP date, determines the number of days that have passed until today, and converts that into weeks and days. It then adds 280 days to your LMP to provide an Estimated Due Date (EDD).

Why LMP, not Conception Date?

While conception is the actual start of fetal development, pinpointing the exact date of conception can be difficult. Ovulation can vary, and sperm can live for several days. The LMP, however, is usually a more reliable and easily remembered date for most women, making it a practical starting point for dating a pregnancy.

Understanding Trimesters

Pregnancy is typically divided into three trimesters, each marked by significant developmental milestones for the baby and changes for the mother:

• First Trimester (Weeks 0-13): This period covers conception, implantation, and the rapid development of major organs. It's often characterized by morning sickness, fatigue, and breast tenderness.
• Second Trimester (Weeks 14-27): Many women find this trimester more comfortable as morning sickness often subsides. The baby grows rapidly, and you might start to feel fetal movements.
• Third Trimester (Weeks 28-40+): The final stretch involves significant weight gain for the baby, preparation for birth, and increasing discomfort for the mother as the baby grows larger.

Important Considerations

This calculator provides an estimate based on averages. Several factors can influence the actual length of your pregnancy and your baby's arrival date:

• Irregular Periods: If your menstrual cycles are irregular, the LMP method may be less accurate.
• Ultrasound Dating: Early ultrasounds (especially between 8-12 weeks) are often considered the most accurate way to date a pregnancy, as they measure the baby's size (Crown-Rump Length – CRL) to estimate gestational age.
• Individual Variation: Only about 5% of babies are born on their exact due date. Most arrive within a week or two before or after.

Always consult with your doctor or midwife for personalized medical advice and the most accurate dating of your pregnancy. This calculator is a helpful tool for general information and estimation.