Pregnancy Calculator
Track how far along you are in weeks and days, your trimester, and weeks remaining, from your last menstrual period.
Formula last reviewed 4 August 2026 · How we verify our calculators
You are
141 weeks 2 days
- Trimester
- 3
- Weeks remaining (of 40)
- 0
- Days since LMP
- 989
Updates live as you type
Frequently asked questions
Pregnancy is counted from the first day of your last menstrual period (LMP), not from conception. So you are considered about two weeks “pregnant” before conception actually occurs.
The first trimester is weeks 1–12, the second is weeks 13–26, and the third runs from week 27 until birth, with full term around 40 weeks.
The LMP is a known, datable event, whereas the exact day of conception is usually uncertain. This is the convention doctors use worldwide.
LMP-based dating is less reliable with irregular cycles. An early ultrasound gives a more accurate gestational age, so rely on your doctor’s assessment.
Weeks and days, not months
Pregnancy is measured in completed weeks and days from the first day of the last menstrual period — "24 weeks and 3 days", not "about six months".
The reason is precision. Fetal development milestones, screening windows and the thresholds that govern clinical decisions are all defined in weeks, and several of them are narrow. A test valid between 11 and 13 weeks plus 6 days has no useful equivalent in months.
How gestational age is counted
Gestational age = days since the first day of the LMP, expressed as completed weeks plus remaining days.
Because dating starts at the LMP rather than conception, gestational age runs roughly two weeks ahead of actual fetal age. At 8 weeks gestational, the embryo has been developing for about 6.
Trimesters are conventionally:
- First — 0 to 13 weeks 6 days
- Second — 14 to 27 weeks 6 days
- Third — 28 weeks to birth
Term is 37 to 42 weeks, subdivided in current obstetric practice into early term (37–38+6), full term (39–40+6), late term (41–41+6) and post-term (42+).
The dated milestones
Several points in pregnancy carry time-bound clinical significance, which is the practical reason for tracking weeks precisely:
Around 6–9 weeks — first antenatal visit and dating scan in most protocols.
11 to 13 weeks 6 days — the nuchal translucency scan and combined first-trimester screening. This window is firm; outside it the test cannot be performed.
Around 18 to 22 weeks — the detailed anomaly scan, examining fetal anatomy. Note that in India, the Pre-Conception and Pre-Natal Diagnostic Techniques (PCPNDT) Act prohibits any disclosure of fetal sex, and this is enforced strictly.
24 to 28 weeks — glucose tolerance testing for gestational diabetes.
28 weeks — anti-D prophylaxis where the mother is Rh negative.
Around 36 weeks — group B streptococcus screening in some protocols, and assessment of fetal position.
What the calculator shows
Weeks and days is the clinical measure. Trimester places it in the conventional three-part division. Weeks remaining counts down to 40 weeks, which is a midpoint rather than an endpoint.
Note that days since LMP can exceed 280 without concern — pregnancies continuing past the due date are common, and most protocols discuss induction somewhere between 41 and 42 weeks rather than at 40.
The limits of this estimate
The calculation assumes a regular 28-day cycle and an accurately recalled LMP. Several situations make it unreliable:
Irregular cycles, where ovulation timing varies and LMP-based dating can be out by a week or more.
Recent hormonal contraception, after which the first cycles are often not representative.
Uncertain LMP, which is common.
Bleeding in early pregnancy mistaken for a period.
In all of these, early ultrasound dating is substantially more reliable and should take precedence.
This is general information, not medical advice. Every pregnancy needs proper antenatal care. Any concern — bleeding, severe pain, reduced fetal movement, severe headache or visual disturbance, or anything that simply feels wrong — warrants contacting a doctor or midwife immediately rather than consulting a calculator.
Common mistakes
Converting weeks to months casually. Nine months and 40 weeks are not the same, and clinical windows are defined in weeks.
Treating gestational age as fetal age. It runs about two weeks ahead.
Missing a screening window. Several are narrow and cannot be performed late.
Assuming 40 weeks is a deadline. It is a midpoint; term extends to 42.
Relying on LMP dating with irregular cycles. An early scan is far more accurate.