Pregnancy Week‑by‑Week Tracker
Enter one date to find your current week, trimester, due date and how big your baby is right now.
Enter a date above to see your results.
Browse any week, 4–42
Tap a week to see baby’s development, what’s happening in your body, and one useful tip.
Week 20
Trimester 2Baby: –
Your body: –
Tip: –
How pregnancy weeks are calculated
Quick answer: Pregnancy is tracked in 40 weeks starting from the first day of your last menstrual period (LMP) — not from conception. Week 40 is your estimated due date, but a baby born anywhere from week 37 to week 42 is considered full term.
Because ovulation and conception usually happen about two weeks after your last period starts, you’re already counted as roughly two weeks pregnant before an egg is even fertilized. This is why “gestational age” (from LMP) and “fetal age” (from conception) are almost always about two weeks apart. Doctors, ultrasounds, and due‑date calculators all use gestational age by default.
A due date calculated this way is an estimate, not a guarantee — it’s typically accurate within a week or two. If your cycles are irregular or you’re unsure of your last period, a first‑trimester ultrasound that measures the baby directly usually gives a more precise estimate than LMP alone.
Trimester breakdown
| Trimester | Weeks | What’s generally happening |
|---|---|---|
| First | 1 – 13 | Major organs and body systems begin forming; morning sickness and fatigue are common. |
| Second | 14 – 27 | Energy often returns; the anatomy scan happens; first movements are usually felt. |
| Third | 28 – 40+ | Rapid weight gain and lung maturation; more frequent checkups as birth approaches. |
Frequently asked questions
How are pregnancy weeks counted?
Pregnancy is measured from the first day of your last menstrual period, not from conception. That means you’re already considered a few weeks pregnant before fertilization actually occurs.
What’s the difference between gestational age and fetal age?
Gestational age counts from your last period and is what’s used for due dates. Fetal age counts from conception, which happens about two weeks later, so it runs roughly two weeks behind gestational age.
How many weeks is a full‑term pregnancy?
A full‑term pregnancy is 39 to 40 weeks. Babies born between 37 and 42 weeks are generally considered term, while birth before 37 weeks is classified as preterm.
When does each trimester start and end?
The first trimester runs from week 1 to week 13, the second from week 14 to week 27, and the third from week 28 until birth, typically around week 40.
How accurate is a due date calculated from my last period?
An LMP‑based due date is an estimate, usually accurate within one to two weeks. An early ultrasound can refine it further, especially if your cycles are irregular.
What if I have irregular periods?
Irregular cycles make LMP‑based dating less reliable. In that case, an early first‑trimester ultrasound that measures the baby directly is usually more accurate.
Can a healthy baby be born before 40 weeks?
Yes. Most babies are born between 37 and 42 weeks, and full‑term babies anywhere in that range are typically healthy. Very few babies actually arrive on their exact due date.
Does this tracker replace medical advice?
No. This tool gives general estimates to help you follow your pregnancy. Always confirm your due date and discuss any concerns with your doctor or midwife.