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Estimate baby's due date using Naegele's rule (LMP + 280 days), adjusted for cycle length, with conception date, trimester boundaries and current week and day.
Health
Generated on May 23, 2026
Estimate baby's due date using Naegele's rule (LMP + 280 days), adjusted for cycle length, with conception date, trimester boundaries and current week and day.
This pregnancy calculator uses Naegele's rule (LMP + 280 days) — the standard obstetric method worldwide — adjusted for your individual cycle length if different from the default 28 days. It gives your estimated due date, probable conception date, trimester boundaries, and current pregnancy progress in weeks and days. This is useful for expecting mothers planning their prenatal schedule, partners and family tracking milestones, and healthcare providers confirming gestational age.
Formula
Due Date = LMP + 280 days + (Cycle Length − 28). Conception date ≈ LMP + 14 days + (Cycle Length − 28).Two pink lines, a sudden quiet, and the very first question that surfaces: when is this baby actually due? You've probably already googled it, gotten a date, and started counting backwards trying to figure out if it makes sense. Here's the honest version. The formula every obstetrician uses — Naegele's rule — assumes you ovulated on day 14 of a perfect 28-day cycle. Most women don't. If your cycles run 30 or 32 days, your real conception happened later than this calculator's default assumption, and your real due date is a few days later too. Enter your true cycle length and the estimate sharpens. Even then, only about 5 percent of babies arrive exactly on the date — roughly 80 percent show up within two weeks either side. So treat this number as a target on the calendar, not a deadline. Book your first prenatal visit around 8 to 10 weeks, where the dating ultrasound will almost always trump anything a formula can give you. Until then, take the folic acid, ease off the qahwa, and let yourself feel however you're feeling — excited, terrified, both at once. All of it is normal.
This pregnancy calculator uses Naegele's rule (LMP + 280 days) — the standard obstetric method worldwide — adjusted for your individual cycle length if different from the default 28 days. It gives your estimated due date, probable conception date, trimester boundaries, and current pregnancy progress in weeks and days. This is useful for expecting mothers planning their prenatal schedule, partners and family tracking milestones, and healthcare providers confirming gestational age. Remember that this is an estimate — only about 5% of babies are born exactly on the due date.
Naegele's rule assumes a standard 40-week (280-day) pregnancy counted from the first day of the last menstrual period — not from conception, because LMP is easier to date precisely. The cycle-length adjustment accounts for the fact that ovulation (and therefore conception) happens later in longer cycles, pushing the due date proportionally later. A woman with a 32-day cycle ovulates around day 18, so her due date falls 4 days later than the standard 28-day assumption.
Key pregnancy milestones by gestational week, counted from the first day of the last menstrual period (LMP).
| Week | Trimester | Days Since LMP | Milestone |
|---|---|---|---|
| 4 | 1st | 28 | Missed period, home pregnancy test positive |
| 8 | 1st | 56 | First prenatal visit, dating ultrasound |
| 12 | 1st | 84 | End of first trimester, lowest miscarriage risk |
| 16 | 2nd | 112 | Gender-revealing ultrasound possible |
| 20 | 2nd | 140 | Halfway point, anatomy scan |
| 24 | 2nd | 168 | Viability milestone, baby could survive outside womb |
| 28 | 3rd | 196 | Third trimester begins, glucose screening |
| 32 | 3rd | 224 | Rapid growth, position typically cephalic |
| 37 | 3rd | 259 | Full-term — safe to deliver |
| 40 | 3rd | 280 | Estimated due date |
| 42 | 3rd | 294 | Postterm — induction usually recommended |
Only ~5% of babies arrive exactly on their due date; ~80% arrive within 2 weeks either side.
The 40-week pregnancy is counted from LMP, not from conception — conception occurs ~2 weeks later, so actual gestation is 38 weeks.
Twin pregnancies typically deliver 2–3 weeks earlier than singletons (around 37 weeks).
The first 12 weeks are the highest-risk period; miscarriage rates drop significantly after the first trimester.
LMP January 1 with a 28-day cycle gives an estimated due date of October 8 the same year.
LMP February 14 with a 30-day cycle gives November 23 — two days later than the standard calculation, reflecting the longer cycle.
A pregnancy currently at 20 weeks marks the start of the second trimester and the halfway point.
The third trimester begins at 28 weeks (day 189 of pregnancy) — a key transition for medical appointments and delivery planning.
A pregnancy past 40 weeks (past due date) is called postterm; after 42 weeks, doctors usually recommend induction for safety.
Twin pregnancies are typically delivered 2–3 weeks earlier than singleton due dates, around 37–38 weeks, though the calculator still uses the standard 40-week estimate.
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