The Pregnancy Calculator helps estimate gestational age and expected due date (EDD) based on your last menstrual period (LMP).
Uses Naegele's rule adjusted for your menstrual cycle length. This calculator also displays fetal development per week, trimester, and important dates throughout pregnancy.
Disclaimer: Results are estimates. For accurate information, consult your doctor or midwife.
Calculator information
📋 How to use this calculator
- Note the date of your Last Menstrual Period (LMP). This is the date of the first day of your last period before becoming pregnant, not the date of intercourse.
- Enter the LMP date in the field provided. The system will automatically calculate your EDD (Estimated Due Date).
- If your cycle is not 28 days, enter your actual cycle length (typically 21-35 days). The calculator will adjust accordingly.
- Click "Calculate". You will receive your EDD, current gestational age (in weeks and days), and trimester.
- Review the result with your midwife/OB-GYN at your first prenatal visit (before 12 weeks) for confirmation via ultrasound.
🧮 Naegele's Rule (EDD based on LMP)
EDD = LMP + 280 days (40 weeks)
- EDD = Estimated Due Date
- LMP = Last Menstrual Period (first day)
- Assumes a regular 28-day menstrual cycle
For non-28-day cycles, adjust: EDD = LMP + 280 + (cycle length - 28). Only about 5% of babies are born exactly on the EDD - a range of 38-42 weeks is still considered normal (term).
💡 Worked example: LMP January 5, 2026, 28-day cycle
Given:- LMP = January 5, 2026
- Cycle = 28 days (Naegele standard)
Steps:- Add 280 days to the LMP.
- 280 days = 40 weeks.
- January 5, 2026 + 40 weeks = October 12, 2026.
Result: EDD is approximately October 12, 2026. As of May 11, 2026, gestational age is about 18 weeks 0 days (second trimester).
❓ Frequently asked questions
Is the EDD the exact date I will give birth?
No. The EDD is a statistical estimate. Studies show only 4-5% of babies are born exactly on their EDD. About 70% are born within 10 days before or after the EDD. Delivery between weeks 37-42 is considered term.
I forgot my LMP. What should I do?
Use your best estimate and confirm with an early ultrasound (before 12 weeks). First-trimester ultrasound measures the fetal Crown-Rump Length (CRL) and can estimate gestational age with ±5 days of accuracy, more reliable than a forgotten LMP.
My cycle isn't 28 days; is the result accurate?
The calculator adjusts the EDD based on your cycle length. But for very irregular cycles (e.g., PCOS with 60+ day cycles or anovulation), consulting your doctor is important since ovulation occurs unpredictably. An early ultrasound will be far more accurate than the formula.
When should prenatal care (ANC) begin?
Ideally as soon as you get a positive pregnancy test or before week 12. ACOG recommends a typical schedule of about 12-14 prenatal visits across pregnancy: every 4 weeks until week 28, every 2 weeks from weeks 28-36, then weekly until delivery. The first visit should include an ultrasound, blood work, and infection screening.
What are the differences between trimesters 1, 2, and 3?
Trimester 1 (0-13 weeks): organ formation, highest miscarriage risk, common nausea. Trimester 2 (14-27 weeks): rapid fetal growth, nausea typically subsides, fetal movements begin. Trimester 3 (28-40 weeks): organ maturation, labor preparation, close monitoring for preeclampsia and placental issues.
📚 Sources & references
Last updated: May 11, 2026