Pregnancy Week & Key Dates

Q: What if my cycles aren’t 28 days?

Use the optional cycle length field to adjust the LMP estimate. Early ultrasound commonly refines dating.

Enter the first day of your last period (LMP) or your conception date. You’ll see current gestational week/day, an estimated due date, trimester stage, and a simple timeline. Info only—this isn’t medical advice.

Date you will enter

LMP Conception

LMP date

Conception date

Average cycle length (optional) If not 28 days, this nudges the LMP-based due date. As-of date (optional) Use if planning ahead or reviewing past notes.

Enter a date above and tap Show week & timeline.

How weeks are counted

Gestational age is traditionally counted from the first day of the LMP. Conception usually occurs about two weeks after LMP in a typical 28-day cycle. Due date from LMP is 280 days; from conception it’s 266 days. Early ultrasound sometimes updates dating; that’s expected.

Trimester guide

Common ranges: weeks 1–12 (first trimester), 13–28 (second), 29–40 (third). Local practice varies; your provider will advise.

Pregnancy week & key dates — quick guide

What this shows

You’ll get your current gestational age (weeks + days), an estimated due date, trimester stage, and a compact timeline of common checkpoints. It’s designed to be clear on both phones and desktops: short paragraphs, bold labels where useful, and straight lines for easy scanning.

LMP vs conception

LMP: mirrors how many clinics date routine care and most week-by-week resources. Conception: we add ~14 days to align with clinical “gestational weeks.” If you used IVF, you can enter fertilization timing; for embryo transfer, some teams subtract embryo age to estimate fertilization.

Typical milestones

Weeks 8–14: Dating/viability window and early booking visit.
Weeks 11–13: Nuchal translucency window (where offered).
Weeks 18–22: Detailed anatomy scan period.
Weeks 24–28: Glucose screening and mid-pregnancy checks.
Late second → third trimester: Visits often become more frequent; plans differ by clinic.

Important context

Due dates are estimates—only a small fraction of births occur exactly on that day. Most arrive in the surrounding weeks. If an early ultrasound and calendar dates don’t match, providers commonly use ultrasound dating. Enter any revised date to realign the timeline.

Not medical advice

This is general information. For concerns such as bleeding, severe pain, fever, or later reduced movements, contact your care team promptly. Multiples, IVF, and medical conditions can shift schedules and milestones.

References: ACOG: Methods for Estimating the Due Date · NHS: Week-by-week guide to pregnancy

Pregnancy week calculator FAQs

Why does gestational age start at the last period?

It anchors dating to a known day. Conception typically occurs ~2 weeks after LMP in a 28-day cycle, so LMP + 280 days gives a due date estimate.

What if my cycles aren’t 28 days?

Use the optional cycle length field to nudge the LMP estimate. Early ultrasound commonly refines dating.

Is the due date the day I will deliver?

It’s an estimate. Many births occur in the weeks around it. Plans near late term vary by provider.

How does IVF change the input?

Use conception mode. For embryo transfer, subtract embryo age (e.g., 5 days) from the transfer date to approximate fertilization.

Is this medical advice?

No. This tool provides general information only. Always follow guidance from your care team.

Pregnancy week and key dates calculator for milestones

Calculate pregnancy week and milestone dates