Pregnancy Calculator

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pregnancy calculator
Last Menstrual Period (LMP)Conception Date
Your Results:
Estimated Due Date:
Current Gestational Age:
Current Trimester:
Days Remaining:
function calculatePregnancy(){var method=document.getElementById('calc_method').value;var dateStr=document.getElementById('start_date').value;var cycle=parseInt(document.getElementById('cycle_length').value);var showSteps=document.getElementById('steps').checked;if(!dateStr||isNaN(cycle)){alert('Please provide a valid date and cycle length.');return;}var startDate=new Date(dateStr);var today=new Date();var dueDate=new Date(startDate);if(method==='lmp'){var adjustment=cycle-28;dueDate.setDate(dueDate.getDate()+280+adjustment);}else{dueDate.setDate(dueDate.getDate()+266);}var timeDiff=dueDate.getTime()-today.getTime();var daysRemaining=Math.ceil(timeDiff/(1000*60*60*24));var conceptionDate=new Date(dueDate);conceptionDate.setDate(conceptionDate.getDate()-266);var gestationalDiff=today.getTime()-(dueDate.getTime()-(280*24*60*60*1000));var gestDaysTotal=Math.floor(gestationalDiff/(1000*60*60*24));var weeks=Math.floor(gestDaysTotal/7);var days=gestDaysTotal%7;var trimester="First";if(weeks>=13&&weeks=27)trimester="Third";document.getElementById('dueDateVal').innerHTML=dueDate.toDateString();document.getElementById('ageVal').innerHTML=weeks+" Weeks, "+days+" Days";document.getElementById('trimesterVal').innerHTML=trimester;document.getElementById('daysVal').innerHTML=daysRemaining<0?"Past Due Date":daysRemaining;if(showSteps){var m="Important Milestones:
";var endT1=new Date(dueDate);endT1.setDate(endT1.getDate()-189);var endT2=new Date(dueDate);endT2.setDate(endT2.getDate()-91);m+="End of 1st Trimester: "+endT1.toDateString()+"
";m+="End of 2nd Trimester: "+endT2.toDateString()+"
";m+="Viability Milestone (24w): "+new Date(dueDate.getTime()-(112*24*60*60*1000)).toDateString();document.getElementById('milestones').innerHTML=m;document.getElementById('milestones').style.display='block';}else{document.getElementById('milestones').style.display='none';}document.getElementById('answer').style.display='block';}

How to Use the Pregnancy Calculator

Finding out your estimated due date (EDD) is one of the first steps in planning for your new arrival. This pregnancy calculator uses standardized medical formulas to estimate when your baby will arrive and tracks your current progress through your trimesters.

To get the most accurate result, follow these steps:

Calculation Method
Choose between your Last Menstrual Period (LMP) or your known Conception Date. LMP is the most common clinical method used by doctors.
Date Input
Select the specific date of your last period or conception. Accuracy here is vital for a correct estimate.
Cycle Length
The default is 28 days. If your cycle is shorter or longer, adjust this field to refine your due date calculation.

How It Works: Naegele's Rule

Most healthcare providers use Naegele's Rule to calculate your due date. This rule assumes a pregnancy lasts exactly 280 days (40 weeks) from the first day of your last menstrual period. Our pregnancy calculator refines this by allowing for adjustments in cycle length.

Due Date = LMP + 280 Days + (Cycle Length – 28 Days)

  • LMP: The first day of bleeding during your last cycle.
  • Gestational Age: Measured from the LMP, meaning you are technically "pregnant" for 2 weeks before conception.
  • Conception Date: Usually occurs 14 days after the LMP in a standard 28-day cycle.

Calculation Example

Scenario: Sarah's last menstrual period started on January 1, 2024. She has a slightly longer menstrual cycle of 30 days.

Step-by-step solution:

  1. Identify LMP: January 1, 2024
  2. Identify Cycle Length: 30 days
  3. Standard 40-week addition: January 1 + 280 days = October 7, 2024
  4. Adjust for cycle: Since her cycle is 2 days longer than the 28-day average (30 – 28 = 2), we add 2 days.
  5. Final Result: October 9, 2024

Common Questions

How accurate is a pregnancy calculator?

While a pregnancy calculator is a great tool for estimation, only about 4-5% of babies are born on their exact due date. Most are born within a window of two weeks before or after the estimated date. Factors like ovulation timing and fetal growth rates can influence the actual birth date.

What if I don't know my LMP?

If your cycles are irregular or you don't track your dates, doctors will often use an early ultrasound (dating scan) to measure the size of the embryo and determine a more accurate gestational age and due date.

Can the due date change?

Yes, it is common for a healthcare provider to adjust your due date after an ultrasound if the measurements significantly differ from the dates calculated based on your last period.

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