Due Date Calculator
Calculate your estimated due date (EDD) based on the first day of your last menstrual period (LMP) using Naegele's rule. Also shows gestational age and trimester information.
This free online due date calculator provides instant results with no signup required. All calculations run directly in your browser — your data is never sent to a server. Enter your values below and see results update in real time as you type. Perfect for everyday calculations, homework, or professional use.
Days since the first day of your last menstrual period
Results
Gestational Age (weeks)
8 weeks
Plus Days
4 days
Trimester
1
Days Until Due Date
220 days
Weeks Remaining
31 weeks
How to Use This Calculator
Enter your input values
Fill in all required input fields for the Due Date Calculator. Most fields include unit selectors so you can work in your preferred unit system — metric or imperial, whichever matches your problem.
Review your inputs
Double-check that all values are correct and that you have selected the right units for each field. Incorrect units are the most common source of calculation errors and can produce results that are off by factors of 2, 10, or more.
Read the results
The Due Date Calculator instantly computes the output and displays results with units clearly labeled. All calculations happen in your browser — no loading time and no data sent to a server.
Explore parameter sensitivity
Try adjusting individual input values to see how the output changes. This is a quick and effective way to develop intuition about how different parameters influence the result and to identify which inputs have the largest effect.
When to Use This Calculator
- •Use the Due Date Calculator for personal health tracking and wellness monitoring, establishing a baseline and tracking changes over time.
- •Use it when recording fitness metrics to track progress toward health or athletic goals.
- •Use it to compare measurements before and after a lifestyle, diet, or training change to quantify the impact.
- •Use it as a conversation starter before a doctor's appointment, bringing objective data to discuss with a healthcare professional.
About Due Date Calculator
The Due Date Calculator estimates your expected delivery date using Naegele's rule, the standard clinical method. It adds 280 days (40 weeks) to the first day of your last menstrual period (LMP). This assumes a 28-day menstrual cycle with ovulation occurring on day 14 — actual conception therefore occurs approximately 266 days before the due date. The calculator also shows current gestational age in weeks and days, trimester, and countdown to the estimated due date. Only about 5% of babies are born on their exact due date; the due date represents the midpoint of a normal delivery window spanning 37-42 weeks.
The Math Behind It
Formula Reference
Naegele's Rule
EDD = LMP + 280 days (40 weeks)
Variables: LMP = first day of last menstrual period
Worked Examples
Example 1: Early Pregnancy
LMP was 60 days ago
Currently 8 weeks 4 days pregnant, 1st trimester, approximately 31 weeks to due date.
Example 2: Third Trimester
LMP was 210 days ago
Currently 30 weeks pregnant, 3rd trimester, approximately 10 weeks to due date.
Common Mistakes & Tips
- !Using the date of conception instead of LMP. Gestational age is always counted from the first day of the last menstrual period, which is approximately 2 weeks before ovulation.
- !Not adjusting for irregular cycles. If your cycle is longer than 28 days, add the extra days to the calculated due date.
- !Treating the due date as exact. Only ~5% of babies are born on the calculated due date. The normal delivery window is 37-42 weeks.
Related Concepts
Used in These Calculators
Calculators that build on or apply the concepts from this page:
Frequently Asked Questions
How accurate is the due date?
Only about 5% of babies arrive on the exact due date. About 80% are born within 2 weeks of it (38-42 weeks). First-trimester ultrasound dating is accurate to within 5-7 days and is more reliable than LMP dating.
What if my cycles are irregular?
Naegele's rule assumes a 28-day cycle. If your cycles are longer, ovulation occurred later than day 14, and your actual due date is later. Ultrasound dating in the first trimester is recommended for women with irregular cycles.
When should I be concerned if I go past my due date?
Post-term pregnancy (beyond 42 weeks) carries increased risk of stillbirth and complications. Most providers recommend induction between 41 and 42 weeks. Going a few days past the due date is extremely common and not a concern.