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
135 weeks 1 days
- Trimester
- 3
- Weeks remaining (of 40)
- 0
- Days since LMP
- 946
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.
"Pregnant" starts counting two weeks before conception did
That's not a mistake in the math — it's the standard convention. An LMP of 1 January 2024, checked at 1 June 2024 (152 days later), works out to 21 weeks and 5 days of pregnancy — placing it in the second trimester (weeks 13–26), with 19 weeks remaining toward the standard 40-week estimate. But gestational age is counted from the first day of your last period, not from conception itself, which typically happens roughly two weeks after that date. In other words, "week 2" of a pregnancy generally falls before an egg was even fertilized.
Why doctors count from LMP instead of conception, everywhere
Conception happens internally and privately, with no reliable external marker — there's no way to date it directly in the vast majority of pregnancies. The last menstrual period, by contrast, is a known, datable event most people can pin down precisely, which is exactly why it became the global obstetric convention for gestational dating rather than a less-certain estimate of the actual conception date.
What the weeks-completed figure actually drives
The trimester breakdown follows directly from weeks completed: first trimester spans weeks 1–12, second runs 13–26, and third continues from week 27 through birth around the 40-week mark. The remaining-weeks countdown simply moves in lockstep — one week further along always means one week less remaining. Worth knowing before treating 40 weeks as a hard deadline: "full term" itself spans a range, with babies born anywhere from 37 to 42 weeks considered full term, so this countdown is a planning guide for milestones, antenatal appointments and scans — not a fixed date your baby is bound to arrive on.
This is an estimate based on standard assumptions, not medical advice. Pregnancy dating and growth can vary — consult your doctor for personalised assessment, especially if cycles are irregular.