Pregnancy Due Date Predictor
Estimate your due date using Naegele's rule — from your last menstrual period or conception date — and see gestational age, trimester stage, and key milestones instantly.
Pregnancy Timeline Inputs
Educational estimate only — not medical/insurance advice. Consult a qualified professional.
Pregnancy Timeline Results
Estimated Due Date
—
based on Naegele's rule
Gestational Age
—
today, in weeks + days
Trimester
—
1st ends wk 13, 2nd wk 27
Days to Due Date
—
remaining from today
Key Milestones
| Week | Milestone | Status |
|---|
Calculation Breakdown
Waiting for input…
Dates are estimates only. Only about 5% of babies arrive on their exact due date. Confirm your dates with a healthcare provider and an early ultrasound.
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How The Due Date Math Works
Naegele's rule, gestational age, and the trimester and milestone timeline explained.
How The Calculation Works
Naegele's rule estimates a due date by adding 280 days (40 weeks) to the first day of the last menstrual period (LMP). The 280 days represent 266 days of fetal development plus about 14 days from the start of the LMP to ovulation. If you know the conception date instead, the calculator adds 266 days — because conception itself happens about two weeks into the cycle. Gestational age (GA) is counted from the LMP: today's GA in weeks and days is simply the elapsed time since the LMP divided into whole weeks and leftover days.
Trimester & Milestone Reference
The pregnancy is conventionally divided into three trimesters. The first trimester runs from week 0 to the end of week 12 (weeks are counted as completed weeks), the second from week 13 through week 27, and the third from week 28 onward. The milestones table marks widely used clinical checkpoints — the first-trimester screening window around weeks 11–13, the anatomy scan near week 20, the third-trimester start at week 28, and the shift to "full term" at week 37.
- First trimester: weeks 0–12
- Second trimester: weeks 13–27
- Third trimester: weeks 28–40+
Troubleshooting & Edge-Case Failure Points
- Irregular cycles: Naegele assumes a 28-day cycle. If your cycle is longer or shorter, ovulation shifts, and the LMP-based estimate becomes less precise — an early ultrasound is the reliable correction.
- Unknown LMP: if the last menstrual period is not remembered, conception-based dating adds 266 days, but recall of conception itself can be uncertain.
- Weeks vs. months: "16 weeks pregnant" means 16 completed weeks (into the 17th). Mixing months and weeks is a common source of confusion when planning appointments.
- Due dates are estimates: only about 5% of babies are born on their exact due date; a normal range of 37 to 42 weeks is expected.
- Future/past dates: the calculator accepts any current date to show gestational age at a chosen point, which is useful for planning scans or leave.
Step-by-Step Instructions
- Choose whether you know the first day of your last menstrual period or the conception date.
- Enter that date, and confirm the current date (or the date you want to evaluate).
- Click "Calculate" to see your estimated due date (LMP + 280 days, or conception + 266 days).
- Read your gestational age in completed weeks and days, and which trimester you are in.
- Scan the milestone table — past milestones are marked "Reached", and the next upcoming one is highlighted.
- Use the Copy button to share your summary with your care team, and always confirm with a healthcare provider.
Related Web Utilities (Silo Hub)
Informative Guides & Helper Articles
Ultimate Guide to Pregnancy Due Date Predictor
How Naegele's rule works, the 280-day pregnancy model, and why ultrasound dating refines your estimated due date.
Read Article →Best Practices for Pregnancy Due Date Prediction
Recalling your LMP accurately, accounting for cycle length, and combining Naegele with early ultrasound confirmation.
Read Article →Common Errors in Pregnancy Due Date Prediction
Confusing conception with LMP, ignoring irregular cycles, and misreading weeks-versus-months throughout pregnancy.
Read Article →Top Optimization Tips for Your Due Date
Using your due date to time scans, plan leave, and coordinate the milestones that matter through all three trimesters.
Read Article →Future Trends in Pregnancy Due Date Prediction
AI-assisted ultrasound dating, home monitoring, and personalized due dates built from biomarkers and real-world birth data.
Read Article →How to Use the Pregnancy Due Date Calculator
Estimates the due date from your last menstrual period or conception date — with the trimester map and the countdown.
- Enter the first day of your last menstrual period (LMP) — the standard input.
- Or enter conception/IVF transfer date if known (more precise).
- Read the estimated due date, current gestational week, and trimester boundaries.
Naegele's Rule and the 40-Week Fiction
The standard estimate is Naegele's rule: LMP + 280 days (40 weeks), calibrated to a 28-day cycle with ovulation on day 14 — adjust a few days for longer or shorter cycles. Two honest caveats: first-trimester ultrasound remains the most accurate dating (it beats LMP recall), and the "due date" is really a due week: only about 4–5% of babies arrive on the exact date, with first babies averaging ~40w5d and most delivering between 37 and 42 weeks — all of it normal. Trimester boundaries: weeks 1–13, 14–27, 28–40+, with viability (~24w) and term reclassification (37–38 early, 39–40 full, 41+ late) as the clinical markers your provider tracks.
Pregnancy Due Date Calculator FAQ
How accurate is a due date?
It is a centered estimate: ~4-5% deliver on the day, most between 37-42 weeks. First-trimester ultrasound is the most accurate dating method.
How is the due date calculated?
Naegele's rule: first day of LMP + 280 days, assuming a 28-day cycle with ovulation on day 14. Shorter/longer cycles shift it.
What is a full-term pregnancy?
39-40 weeks is "full term"; 37-38 is early term, 41+ late term, 42+ post-term. Babies are not late at 40 weeks - that is the center, not a deadline.