WeekTracker

Pregnancy Week Calculator

Current week, days into it, and trimester.

First day of last period (LMP)

Weeks: —
Days into current week: —
Trimester: 3 of 3

What you entered

LMP:

1
Days elapsed since LMP
today − LMP= — days
2
Convert to weeks and remainder days
— ÷ 7= — weeks, — days
3
Determine trimester
1st: weeks 0–12 · 2nd: weeks 13–26 · 3rd: weeks 27+= Trimester 3

Result

Current week: — weeks, — days

You're — weeks and — days along, in trimester 3.

Gestational age and trimester by days since your last period

Pregnancy is dated from the first day of the last menstrual period, not from conception, which is why week 1 predates conception by about two weeks.

Days since last period	Gestational age	Trimester
54 days	7 weeks 5 days	First
98 days	14 weeks 0 days	Second
159 days	22 weeks 5 days	Second
218 days	31 weeks 1 day	Third
245 days	35 weeks 0 days	Third

Dating from a last menstrual period assumes a regular 28-day cycle and ovulation on day 14. An early ultrasound is more accurate, and your midwife or doctor's date is the one to plan around. The first trimester runs to week 13, the second to week 27, and the third to birth.

Why pregnancy is dated from the last period, not conception

Since conception date is rarely known precisely, medical convention counts pregnancy weeks starting from the first day of the last menstrual period — meaning you're already considered about 2 weeks pregnant before conception typically occurs.

Trimester boundaries

The first trimester runs through week 13, the second through week 27, and the third continues to birth around week 40 — each trimester marks a different phase of fetal development and typical maternal symptoms.

Frequently asked questions

How do I count pregnancy weeks?

Start counting from the first day of your last menstrual period (LMP), not from conception. Week 1 begins on your LMP date. If your LMP was June 1 and today is August 10, you're 10 weeks pregnant (70 days ÷ 7). Your doctor uses the same counting method.

How many weeks is a full-term pregnancy?

Full term is 39–40 weeks. Early term is 37–38 weeks. Late term is 41 weeks. Post-term is 42+ weeks. Most doctors recommend induction by 41–42 weeks due to increased risk of complications. Only about 5% of babies arrive on their exact due date (40 weeks).

What trimester am I in?

First trimester: weeks 1–13 (months 1–3). Second trimester: weeks 14–27 (months 4–6). Third trimester: weeks 28–40 (months 7–9). The second trimester is often called the 'honeymoon phase' — morning sickness typically subsides and energy returns before the discomfort of the third trimester.