Pregnancy Due Date Calculator
Calculate your estimated due date (EDD) by entering the first day of your last menstrual period (LMP). Based on Naegele's rule (LMP + 280 days). Also shows your current pregnancy week and trimester. Free and private.
Key Capabilities
Naegele's Rule EDD from LMP
Calculates the estimated due date by adding exactly 280 days to the first day of your last menstrual period — the same Naegele's Rule formula used by obstetricians and midwives globally.
Current gestational age in weeks and days
Shows how many weeks and days pregnant you are today and identifies your current trimester: First (weeks 1–13), Second (weeks 14–26), or Third (weeks 27 onwards).
Entirely client-side — no personal dates transmitted
LMP dates are sensitive health information. All date arithmetic runs in your browser. No dates or personal details are ever sent to any server.
How to Use
Enter the first day of your last menstrual period
Select the date using the date picker. Use the first day of bleeding of your most recent period before conception.
View your estimated due date
The EDD appears immediately as LMP plus 280 days. About 5% of babies are born on their exact EDD — a two-week window either side is normal.
Check your current week and trimester
The tool shows how many weeks and days pregnant you are today. Confirm this with your healthcare provider's dating ultrasound when available.
Common Use Cases
- Newly pregnant women awaiting their first scanA woman who has just received a positive pregnancy test enters her LMP to get an initial EDD and know which trimester she is in before her booking appointment with a midwife.
- Expectant fathers planning paternity leaveA father calculates the EDD and works backward to identify when paternity leave should begin, allowing early workplace planning without disclosing the pregnancy to HR prematurely.
- Antenatal nurses during initial phone consultationsA midwife taking a first booking call quickly verifies gestational age and EDD from the patient's reported LMP before the formal dating ultrasound is scheduled.
Frequently Asked Questions
How is the due date calculated?
The tool uses Naegele's Rule — the most widely used method in clinical practice. It adds 280 days (40 weeks) to the first day of your last menstrual period (LMP). This assumes a standard 28-day cycle with ovulation on day 14.
How accurate is the LMP due date?
About 80% of pregnancies deliver within 2 weeks of the calculated EDD. Accuracy depends on cycle regularity. An ultrasound dating scan in the first trimester (7–12 weeks) provides the most accurate EDD and should be used when available.
What are the trimester boundaries?
First Trimester: weeks 1–13. Second Trimester: weeks 14–26. Third Trimester: weeks 27–40+. Most healthcare providers adjust these definitions slightly based on clinical context.
Related Tools
BMI Calculator
Calculate your Body Mass Index (BMI) using metric (kg/cm) or imperial (lbs/inches) measurements. Instantly see your WHO weight category. Free, private, and runs entirely in your browser with no uploads.
Medication Dosage Calculator
Calculate weight-based medication doses for adults and paediatric patients. Enter the patient's weight, the prescribed dose rate in mg/kg, and administration frequency to calculate single-dose and total daily amounts. For reference only — always verify with a pharmacist or physician.