Pregnancy Calculator
Find out when you got pregnant or calculate your due date from your last period or conception date. Includes trimester info and key pregnancy milestones.
About the Pregnancy Calculator
Knowing when conception occurred and when your baby is due are two of the most important dates in any pregnancy. Our pregnancy calculator works in two directions: you can enter your last menstrual period (LMP) or a known due date to calculate the estimated conception window, or enter your LMP or conception date to calculate your expected due date. The tool also tells you how many weeks pregnant you currently are, which trimester you are in, and key upcoming milestones.
Standard obstetric dating starts from the first day of your last menstrual period, even though conception typically occurs about 14 days later (at ovulation). This is a medical convention — because LMP is easier to pinpoint than ovulation, clinicians use it as the start of gestational age. A full-term pregnancy is 40 weeks from LMP, meaning conception accounts for weeks 1–2 and the embryo/fetus develops across weeks 3–40. Your due date is LMP + 280 days (or conception date + 266 days).
Pregnancy is divided into three trimesters: the first runs from weeks 1–12, the second from weeks 13–26, and the third from weeks 27–40. Each trimester brings distinct developmental milestones. The first trimester covers all major organ formation; the second is when most parents find out the sex of the baby and feel first movements; the third involves rapid weight gain and lung maturation in preparation for birth. Our calculator shows the trimester you are in and a timeline of key milestone weeks.
Pros & Cons
- +Works from either LMP or conception date to find due date or conception date
- +Shows current gestational week and trimester
- +Displays key pregnancy milestones (anatomy scan, viability, full term)
- +Visual pregnancy timeline for easy progress tracking
- +Helpful for both early confirmation and ongoing pregnancy management
- −Based on a standard 28-day menstrual cycle — irregular cycles affect accuracy
- −All dates are estimates; only an ultrasound can confirm gestational age precisely
- −Does not account for assisted reproduction (IVF) cycle differences
- −Not a medical tool — always consult a healthcare provider for clinical guidance
- −Milestones shown are population averages; individual pregnancies vary
How Pregnancy Dating Works
Gestational age is measured in weeks from the first day of the last menstrual period. This means that at the moment of conception (roughly week 2), you are already considered two weeks pregnant by the clinical standard. While this seems counterintuitive, it is the universal medical convention because LMP is reliably recalled while ovulation timing varies and is rarely observed directly.
The first trimester (weeks 1–12) is the period of greatest developmental change. The fertilised egg implants in the uterine wall, the placenta forms, and all major organ systems — heart, brain, spinal cord, limbs — are laid down. The embryo becomes a fetus at week 8, by which point it has recognisable human features. This trimester carries the highest risk of miscarriage, which is why many couples wait until the end of the first trimester (the 12-week scan) to announce a pregnancy.
The second trimester (weeks 13–26) is generally considered the most comfortable period. Morning sickness typically eases, energy levels improve, and the pregnancy becomes visible externally. The anatomy scan at around week 20 checks for structural abnormalities and can reveal the baby's sex. At week 24, the fetus reaches the threshold of viability — the earliest point at which survival outside the womb is possible with intensive medical support.