Pregnancy Week Calculator by Due Date
Enter your estimated due date to calculate your current pregnancy week, gestational age in weeks and days, trimester, and key timeline milestones.
How to use this pregnancy week by due date calculator
This tool is designed for people who already know their estimated due date and want to quickly convert it into a pregnancy week for today (or any date you choose). It is especially useful for planning appointments, understanding trimester timing, and tracking your timeline in a simple way.
- Choose your estimated due date.
- Select a reference date (today is filled in by default).
- Click Calculate Pregnancy Week to see gestational age and milestone dates.
How the calculation works
In obstetrics, pregnancy is commonly dated as 40 weeks (280 days) from the first day of the last menstrual period (LMP), not from conception. If you enter a due date, we estimate backwards to find LMP and then count forward to your selected date.
Core formula
- Estimated LMP = Due Date − 280 days
- Gestational age in days = Reference Date − Estimated LMP
- Gestational age in weeks = floor(days ÷ 7), plus remaining days
What your result means
Weeks and days
Your result appears as completed weeks and extra days (for example, 23 weeks and 4 days). This is the most common clinical way to describe pregnancy progress.
Trimester estimate
- First trimester: 0 weeks 0 days to 13 weeks 6 days
- Second trimester: 14 weeks 0 days to 27 weeks 6 days
- Third trimester: 28 weeks 0 days to birth
When a due-date-based calculator is most useful
- You received a due date from an ultrasound or clinician and want quick week-by-week tracking.
- You need a simple estimate for forms, pregnancy apps, or planning.
- You want to understand important timeline markers like 12, 20, 28, and 37 weeks.
Frequently asked questions
Can my due date change?
Yes. Providers may adjust due date based on early ultrasound measurements, cycle history, and clinical findings. If your provider gives you an updated due date, use that date for more accurate week estimates.
Is this the same as conception age?
No. Gestational age is usually about two weeks ahead of conception age because it starts from LMP. This calculator uses standard gestational dating.
Can this tool replace prenatal care?
No. This is an educational calculator. Always rely on your healthcare professional for diagnosis, medical decisions, and individualized pregnancy guidance.
Related search topics
If you are comparing tools, you may also look for: gestational age calculator by due date, pregnancy weeks calculator, weeks pregnant from due date, pregnancy timeline calculator, trimester calculator, and due date to pregnancy week converter.