pregnancy by due date calculator

How this pregnancy by due date calculator works

A due date pregnancy calculator works backward from your estimated due date. In clinical settings, a full-term pregnancy is often measured as 280 days (40 weeks) from the first day of the last menstrual period (LMP), or about 266 days from conception. By entering your due date, this calculator estimates where you are in pregnancy for any date you choose.

This is helpful if you already have a due date from your provider and want to answer practical questions such as:

• How many weeks pregnant am I right now?
• When was my estimated conception date?
• What trimester am I in?
• When do common prenatal milestones typically occur?

What your results mean

1) Estimated LMP date

Your estimated LMP is calculated as 280 days before your due date. This does not always equal your actual menstrual start date, but it is the standard anchor for gestational age calculations.

2) Estimated conception date

The calculator estimates conception as roughly 266 days before due date (or about 14 days after LMP in a typical cycle). Real-world conception can vary by several days, so think of this as an approximate window.

3) Gestational age by date

Gestational age is shown in weeks + days. For example, “22 weeks, 3 days” means 157 days have passed since estimated LMP. This is the format clinicians use in prenatal care notes and ultrasound reports.

4) Trimester and progress

Trimesters are grouped into broad phases:

• First trimester: 0 to 13 weeks + 6 days
• Second trimester: 14 to 27 weeks + 6 days
• Third trimester: 28 weeks to due date

Your progress bar estimates how far you are through a 40-week pregnancy model.

Typical pregnancy timeline from due date

Once a due date is known, common milestones can be estimated:

• Weeks 11–13: first trimester screening window
• Weeks 18–22: anatomy ultrasound window
• Weeks 24–28: glucose screening period
• Weeks 35–37: Group B strep testing window
• Week 39 onward: considered full term

Your provider may adjust testing dates based on personal history, local guidelines, and ultrasound findings.

Why your due date may change

Early ultrasound can refine estimated gestational age, especially when cycle length is irregular or LMP is uncertain. If your due date is updated, your pregnancy week and milestone calendar shift accordingly. This is normal and very common.

Tips for using this calculator

• Use the most recent due date given by your healthcare team.
• Recheck milestones after any due date revision.
• Remember this is an estimate for planning, not a substitute for prenatal care.
• If you have pain, bleeding, or urgent symptoms, contact your provider immediately.

Frequently asked questions

Is this calculator accurate?

It is accurate for standard date math based on a 40-week model. Biological timing varies from person to person, so estimated conception and milestone dates are approximate.

Can I calculate pregnancy week by due date only?

Yes. If you have a due date, you can estimate your pregnancy week on any date by counting forward from estimated LMP. That is exactly what this tool does automatically.

What if my cycle is not 28 days?

Cycle variation can affect conception timing, but many clinicians still track gestational age by the standardized obstetric method. Your provider may adjust your timeline with ultrasound data.

Does this predict labor day exactly?

No calculator can guarantee delivery day. Most births happen within a range around the due date. The due date is best viewed as a planning anchor, not a fixed appointment.

Medical note: This page is for educational use only and is not medical advice.