Pregnancy Week Calculator (By Due Date)
Enter your estimated due date to calculate how many weeks pregnant you are, your trimester, and key milestone dates.
This tool uses a standard 40-week pregnancy model (280 days from LMP). Always confirm dating with your healthcare provider.
How this pregnancy week calculator works
This pregnancy week calculator by due date estimates your current gestational age using one key input: your estimated due date (EDD). From that date, it counts backward using the standard obstetric timeline.
- Full-term pregnancy length: 280 days (40 weeks) from last menstrual period (LMP)
- Estimated conception date: roughly 266 days before due date
- Gestational week today: based on how far you are from the due date
If your due date is accurate, this gives a quick snapshot of where you are in pregnancy right now.
What you get from the calculator
After calculation, you’ll see:
- Your current pregnancy week + day (for example, 24 weeks and 3 days)
- Your current trimester
- Days remaining until due date (or days past due date)
- Estimated LMP date
- Estimated conception date
- Approximate dates when 2nd and 3rd trimesters begin
Trimester ranges at a glance
First trimester
Week 1 through week 12 (up to 12 weeks + 6 days). This is when early fetal development and many first symptoms occur.
Second trimester
Week 13 through week 26 (up to 26 weeks + 6 days). Many people feel more energy, and anatomy scans usually happen in this period.
Third trimester
Week 27 to birth. Growth accelerates, prenatal visits become more frequent, and labor preparation begins.
Why due-date-based dating is useful
Many parents remember their due date but not exact LMP details. A due-date pregnancy calculator is helpful because it quickly translates one memorable date into practical milestones you can use for appointments, planning leave, and understanding fetal development stages.
Important notes about accuracy
- Due dates are estimates—not guarantees of delivery day.
- Early ultrasound can adjust your due date if fetal size suggests different dating.
- Cycle length variations can shift ovulation and conception timing.
- This calculator supports planning, not diagnosis.
Frequently asked questions
Can I calculate pregnancy week if my due date changed?
Yes. Just enter your updated due date and recalculate. The newest clinically confirmed due date is typically the best one to use.
Does this tool work if I’m past 40 weeks?
Yes. If your due date has passed, the result will show how many days overdue you are and continue counting gestational age.
What if the result says the pregnancy hasn’t started yet?
That means your selected “calculate as of” date is earlier than the estimated LMP date implied by your due date.
Is this the same as a conception calculator?
Not exactly. This is primarily a gestational age calculator from due date. It also gives an approximate conception date as a secondary estimate.