Pregnancy Due Date Weeks Calculator
Enter your due date to estimate how many weeks pregnant you are on a chosen date, plus weeks remaining until delivery.
Educational tool only. Always confirm dates and care plans with your OB-GYN or midwife.
What this due date weeks calculator does
This due date weeks calculator helps you quickly estimate your gestational age from your expected due date. Many people search for terms like how many weeks pregnant am I, pregnancy week calculator, and gestational age calculator. This tool is designed for exactly that purpose.
Using your due date and a reference date (today by default), it estimates:
- Your current pregnancy age in weeks and days
- How long until your due date
- Estimated last menstrual period (LMP)
- Estimated conception date
- Current trimester
How the calculation works
Most pregnancies are measured as 40 weeks (280 days) from the first day of the last menstrual period. If your due date is known, the calculator works backward from that date to estimate pregnancy timing.
Core formula
- Gestational age in days = 280 − (days until due date)
- LMP estimate = due date − 280 days
- Conception estimate = due date − 266 days
Because cycle lengths and ovulation timing vary, these are estimates, not exact biological timestamps.
How to use this pregnancy weeks tool
Step 1: Enter your estimated due date
You can usually get this from your provider, ultrasound report, or prenatal portal.
Step 2: Pick a reference date
If you leave the second date blank, the calculator uses today. You can also choose a future date to see how many weeks pregnant you will be later.
Step 3: Click “Calculate Weeks”
You’ll get a clear result showing your pregnancy timeline and key estimated dates.
Understanding your result
Your result includes a pregnancy age like “22 weeks 3 days.” That means 22 full weeks have been completed, plus 3 days into the next week.
- First trimester: up to 13 weeks 6 days
- Second trimester: 14 weeks to 27 weeks 6 days
- Third trimester: 28 weeks to birth
If your due date has passed, the calculator will show how many days or weeks overdue the pregnancy is, based on your selected reference date.
Why due dates can change
It’s normal for estimated due dates to be adjusted, especially early in pregnancy. A few common reasons:
- Irregular or longer menstrual cycles
- Unknown ovulation date
- First-trimester ultrasound providing a more accurate fetal measurement
- Initial date entered from memory rather than documented records
For clinical decisions, your provider’s dating method is always the correct source.
Quick pregnancy timeline reference
- 8 weeks: early prenatal checkups and labs are common
- 12 weeks: end of first trimester approaches
- 20 weeks: anatomy scan period
- 28 weeks: third trimester begins
- 36 weeks: more frequent visits usually begin
- 40 weeks: estimated due date
FAQ
Is this the same as a due date calculator from conception date?
Not exactly. This page starts from your due date and works backward. A conception-based calculator starts from conception and works forward.
Can this replace a prenatal appointment?
No. It is an educational estimate. Medical dating, fetal growth checks, and treatment decisions must come from your healthcare team.
Why does my week count look different from an app?
Different tools may round days differently or label “current week” in different ways. Always prioritize your provider’s official dating.
Medical note
If you have pain, bleeding, contractions, reduced fetal movement, or any urgent concern, contact your clinician or emergency services immediately. Online tools are supportive, but not diagnostic.