Pregnancy Calculator
Calculate your due date, current week, trimester and key pregnancy milestones
Pregnancy is dated from the first day of your last period, not from conception.
Results & Details
// Trimester Progress
// Key Milestones
// Week-by-Week Timeline
| Week | Trimester | Date Range |
|---|---|---|
| Enter a date above to see timeline | ||
How Due Date Is Calculated
A standard pregnancy lasts approximately 280 days (40 weeks) from the first day of the last menstrual period (LMP). This is known as Naegele's Rule. Because ovulation typically occurs around day 14 of a 28-day cycle, the actual time since conception is about 266 days (38 weeks).
Naegele's Rule
Add 280 days (40 weeks) to the first day of the last menstrual period. For cycles longer or shorter than 28 days, the due date is adjusted by the difference. For a 30-day cycle, 2 days are added; for a 26-day cycle, 2 days are subtracted.
The Three Trimesters
First trimester (weeks 1–13): Organ formation, highest miscarriage risk, morning sickness common. Nuchal translucency scan typically at weeks 11–14.
Second trimester (weeks 14–27): Often the most comfortable period. Anomaly scan at weeks 18–21. Baby begins moving (quickening) around weeks 16–20.
Third trimester (weeks 28–40): Rapid growth phase. Baby gains most of its birth weight. Full term is considered 37–42 weeks.
IVF Due Date
For a 5-day blastocyst transfer, the equivalent LMP date is calculated as transfer date minus 17 days (since a 5-day blastocyst is equivalent to 5 days past ovulation, and ovulation occurs 14 days after LMP). For a 3-day embryo transfer, subtract 19 days from the transfer date.
How Accurate Is the Due Date?
Only about 5% of babies are born on their exact due date. Most are born within 2 weeks either side. Ultrasound measurements in the first trimester are the most accurate way to confirm gestational age, often adjusting the LMP-based estimate.
Due Dates: How They're Calculated and How Much to Trust Them
Built and verified by Andrius R. · Updated June 2026
A due date looks like a prediction; it's really a statistical anchor. Knowing how the number is built — and how wide its error bars are — makes the whole pregnancy calendar easier to read. (And the standing caveat for everything below: this calculator estimates; your midwife or doctor confirms.)
Naegele's rule: the 280-day convention
The standard method counts 280 days (40 weeks) from the first day of the last menstrual period (LMP): due date ≈ 8 June 2026. The classic shortcut gives the same answer: LMP + 7 days − 3 months + 1 year.
The quirk everyone notices eventually: pregnancy is counted from the LMP, roughly two weeks before conception (which typically occurs near ovulation, ~day 14). So at "4 weeks pregnant" the embryo is about 2 weeks old, and nobody is ever really pregnant during weeks 1–2. The convention survives because the LMP is a date most people know, while conception usually isn't.
How accurate is it?
Honestly: it's a center of gravity, not an appointment. Only about 4–5% of babies arrive on their due date; roughly two-thirds arrive within a week of it, and ~90% within two weeks. "Full term" is itself a window — 39 weeks 0 days to 40 weeks 6 days, with 37–38 weeks called early term and 41+ late term. Naegele's rule also assumes a textbook 28-day cycle with day-14 ovulation; longer or irregular cycles shift the estimate, which some calculators (including this one) adjust for. The most accurate dating tool is the first-trimester ultrasound — measuring the embryo's crown-rump length dates a pregnancy to within ~5–7 days, and clinical guidance (ACOG) prefers it over the LMP date when the two disagree meaningfully. If your scan gives a different due date than this page, the scan wins.
The trimester map, with dates from the example
| Stage | Weeks | Example dates | Landmarks |
|---|---|---|---|
| First trimester | 1–13 | 1 Sep – 1 Dec 2025 | Organ formation; dating scan ~8–14 wks; miscarriage risk falls sharply after wk 12 |
| Second trimester | 14–27 | to 9 Mar 2026 | Anomaly scan ~18–22 wks; first movements ~16–25 wks; usually the easiest stretch |
| Third trimester | 28–40+ | to ~8 Jun 2026 | Rapid growth; head-down ~32–36 wks; "term" from 37 wks |
Reading pregnancy math like a clinician
- "Weeks + days" notation: 32+4 means 32 weeks and 4 days from LMP — the unit charts and midwives actually use; months are too lumpy for medicine.
- 40 weeks ≠ 9 months: 280 days is closer to 9¼ calendar months or exactly 10 lunar months — the source of endless "9 months" confusion.
- Counting down: gestational age counts up from LMP; "weeks to go" counts down from the due date. The two always sum to 40 — a handy cross-check on any week number you're given.
None of this replaces antenatal care: bleeding, severe pain, reduced movements or anything worrying warrants contacting your provider regardless of what week the calendar says.
// First Appointment
Book your first antenatal appointment (booking appointment) as soon as possible — ideally before 10 weeks.
// Folic Acid
Take 400 mcg of folic acid daily from before conception until 12 weeks to reduce the risk of neural tube defects.
// Nuchal Scan
The nuchal translucency scan (11–14 weeks) screens for chromosomal conditions including Down's syndrome.
// Full Term
Full term is 37–42 weeks. Babies born before 37 weeks are considered premature; after 42 weeks, post-term.