How far along you are — your gestational age — is counted from the first day of your last menstrual period, not from conception. Take the number of days from that day to today and divide by seven for the weeks, with the remainder as extra days. Weeks 1–12 are the first trimester, 13–28 the second and 29–40 the third, and the due date is 40 weeks (280 days) from the last period. Enter your last period and the calculator works out your weeks, days, trimester and due date.
Pregnancy Calculator — how far along am I?
From a last period on Jan 1, 2026, measured on Jan 1, 2026.
- Extra days
- 0
- Trimester
- 1 — First trimester
- Estimated due date
- Oct 8, 2026
Quick examples
How it's calculated
- Gestational age = as-of date − first day of last period
- asOf
- = 20,454
- lmp
- = 20,454
- 0
How it works
Gestational age is how doctors describe the length of a pregnancy, and — per the Office on Women's Health — it is measured from the first day of your last menstrual period (LMP). So a pregnancy described as "13 weeks 1 day" means 13 weeks and 1 day have passed since the LMP, even though conception happened about two weeks after that.
The calculator counts the days from your LMP to the chosen date, divides by seven for the completed weeks, and keeps the remainder as extra days. It then places you in a trimester using the standard week ranges:
- First trimester — weeks 1 to 12
- Second trimester — weeks 13 to 28
- Third trimester — weeks 29 to 40
The due date is 40 weeks (280 days) from the LMP. Gestational age and the due date are estimates that a provider may refine with an early ultrasound; use this as a guide, not a diagnosis.
Worked example
If your last period began on October 1, 2025 and today is January 1, 2026, that is 92 days. Dividing by seven gives 13 weeks with 1 day left over — so you are 13 weeks 1 day along, in the Second trimester. Your estimated due date is Jul 8, 2026, which is 280 days after the last period.
Frequently asked questions
How many weeks pregnant am I?
- Count the days from the first day of your last period to today and divide by seven. The whole number is your weeks and the remainder is extra days. For example, 92 days is 13 weeks and 1 day.
Is gestational age measured from conception?
- No. Gestational age is measured from the first day of your last menstrual period, which is about two weeks before conception. This is the standard clinical convention because the LMP is an identifiable date.
Which trimester am I in?
- Counting from your last period, weeks 1–12 are the first trimester, weeks 13–28 the second and weeks 29–40 the third. The calculator shows your current trimester based on your gestational age.
How is the due date related to how far along I am?
- The due date is 40 weeks (280 days) from your last period, so your weeks pregnant plus the weeks remaining until the due date always add up to 40. As gestational age increases, the time to the due date shrinks by the same amount.
Why might my dates differ from my doctor's?
- Providers often adjust dating with an early ultrasound, which measures the baby directly. If your cycle is longer or shorter than average, ovulation and conception shift, which can move your gestational age by a few days.
Can I check a past or future date?
- Yes. The calculator uses today by default, but you can set any "as of" date to see how far along the pregnancy was, or will be, on that day.
How we know this is right
- Last reviewed
- Aug 7, 2026
- Precision
- Rounded to 0 decimal places.