Health

Pregnancy Due Date Calculator · Gestational Age & Trimester

Enter your LMP (last menstrual period) to instantly get due date (Naegele's rule · LMP + 280 days), current gestational age (w+d), trimester (1st/2nd/3rd), countdown, and estimated conception date. Non-28-day cycles auto-adjusted. All local.

Overview

Due date is the anchor of the whole pregnancy timeline. We use Naegele's Rule: LMP + 280 days = due date. Tool also reports current gestational age (w+d), trimester (1st ≤12w / 2nd 13-27w / 3rd ≥28w, post-term >42w), countdown, cycle-adjusted due date, and estimated conception (LMP+14d). Fully client-side.

How to use

Pick your LMP (day flow started, not ended).
If your cycle is not 28 days (e.g. 35), update it — due date shifts accordingly.
The "Reference date" defaults to today; change to see past/future gestational age.
Panel shows due date, gestational age, trimester, and countdown.

Formula

EDD = LMP + 280 days (28-day cycle baseline); adjust by (cycle − 28) for other cycles.
Gestational age: total days from LMP; weeks = floor(days/7), days = days mod 7.
Trimesters: ≤12w first, 13-27w second, 28-42w third, >42w post-term.
Estimated conception = LMP + 14 days (± cycle offset).

Common scenarios

Standard 28-day cycle

LMP 2026-01-01, today 2026-04-20 → 15w5d, second trimester, 172 days to go.

Long 35-day cycle

LMP 2026-01-01, cycle 35d → due 2026-10-15 (+7 days vs baseline); ovulation is 7 days later.

Just past 12w

LMP 2026-01-01, today 2026-03-27 → 12w1d. Now in 2nd trimester; standard NT scan window (11-13w6d).

FAQ

Is the due date exact?

Only ~5% of babies are born on the exact due date. Early (8-13w) CRL ultrasound is more accurate than LMP calc; doctors usually use that as the official due date.

What if my cycle is not 28 days?

Ovulation shifts with cycle length. Tool adjusts due date by (cycle − 28) days. For highly irregular cycles (e.g., PCOS), rely on ultrasound.

How are trimesters defined?

Per WHO: 1st 0-12w (organ formation), 2nd 13-27w (feel-movement, 4-weekly visits), 3rd ≥28w (rapid growth). >42w = post-term, consult OB immediately.

When should I start antenatal care?

First ultrasound at 6-8w to confirm intrauterine pregnancy. Register (big card) around 12w. NT scan 11-13+6w, combined/NIPT 15-20w, OGTT 24-28w, anatomy scan 20-24w.

Is the estimated conception date exact?

Only an estimate. Actual conception is within 24-72h of ovulation, and ovulation itself has ±2-3 days variability. Not to be used for paternity or legal inference.

Is my LMP data uploaded?

No. Everything runs locally; nothing leaves your device. You can use it offline.