Pregnancy Due Date Calculator
Enter your last period date or conception date to instantly calculate your estimated due date, how many weeks pregnant you are, and which trimester you’re in.
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Calculate your estimated due date, weeks pregnant, and trimester from your last period or conception date.
What Is My Pregnancy Due Date — and How Is It Calculated?
Your estimated due date (EDD) is one of the first things you want to know the moment you see a positive test. It tells you when to expect your baby and gives structure to prenatal appointments, screening schedules, and birth planning — all anchored to a single date.
This pregnancy due date calculator uses Naegele’s Rule — the standard clinical method used by doctors and midwives — to calculate your EDD from your last menstrual period date. You can also enter a known conception date if you tracked ovulation.
Real Example: Calculating Pregnancy Due Date
That’s it — LMP + 280 days = estimated due date. This is Naegele’s Rule, and it’s been the clinical standard for over 200 years.
The Due Date Formula — Naegele’s Rule
Pregnancy Trimesters — What Happens When
| Trimester | Weeks | Months | Key milestones |
|---|---|---|---|
| First | 1–12 | 1–3 | Heartbeat (wk 6), organ formation, highest miscarriage risk |
| Second | 13–27 | 4–6 | Baby moves (wk 16–18), sex visible, viability ~22 weeks |
| Third | 28–40+ | 7–9+ | Lungs mature, head engages, labour and delivery |
How Accurate Is a Due Date Calculator?
The LMP-based due date assumes a 28-day cycle with ovulation on day 14. Only about 5% of babies are born on their exact estimated due date. Most births occur within 2 weeks on either side. Factors that affect accuracy:
- Irregular cycles — if your cycle is consistently longer or shorter than 28 days, the calculator adjusts, but real variation within cycles is harder to account for
- Early ultrasound — a scan before 13 weeks (crown-rump length measurement) is more accurate than LMP-based calculation
- Known conception date — if you tracked ovulation and know when you conceived, use the conception date option for a potentially more accurate estimate
✍️ Reviewed by the NerdyTools Health Team — Last updated August 2026. This tool is for informational purposes only.
Due-Date Estimates and Pregnancy Dating
A calculated due date is an estimate based on the date of the last menstrual period or conception assumption. Ovulation timing, cycle length, implantation, ultrasound measurements, and clinical dating can shift the estimate. Most babies are not born on the exact due date, and the result should not be used to schedule medical care without your clinician. Contact a qualified healthcare professional for pregnancy questions, warning signs, or the official gestational age used in your records.
Frequently Asked Questions
Sources & References
Calculations verified against authoritative sources: ACOG — Methods for Estimating Due Date
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