Pregnancy Due Date Calculator
Enter the date of your appointment or scan and the gestational age on that same date. This calculator estimates your expected due date (40 weeks / 280 days).
Educational use only. Always confirm dates with your OB-GYN or midwife.
How this due date calculator by weeks gestation works
This tool calculates an estimated due date using one core idea: full-term pregnancy is approximately 40 weeks (280 days) from the first day of the last menstrual period (LMP). If you already know gestational age on a specific date, we can work backward and forward from that information to estimate key pregnancy dates.
For example, if you are 16 weeks and 2 days pregnant on May 1, the calculator determines how many days remain until 40 weeks and adds that to May 1. That produces your estimated delivery date (EDD).
When to use this calculator
A weeks-gestation due date calculator is useful when:
- You were given a gestational age at an ultrasound visit.
- You know how far along you were at a prenatal appointment.
- You want a quick estimate before your next provider visit.
- You are tracking milestones such as trimester changes or full-term status.
What the result includes
After calculating, you will see:
- Estimated Due Date (EDD)
- Estimated LMP date based on 280 days before EDD
- Estimated conception date (roughly 14 days after LMP)
- Days remaining or how many days past the due date
- Milestone dates such as 12, 20, 28, and 37 weeks
Important accuracy notes
1) A due date is an estimate, not a guarantee
Most babies are not born exactly on the estimated due date. Birth commonly occurs within a range around that date. The EDD is best treated as a planning target, not a fixed deadline.
2) Ultrasound timing matters
First-trimester ultrasounds are generally considered more precise for dating than later scans. If your provider gives you a revised due date based on early imaging, follow the provider's date.
3) Individual factors can shift timing
Cycle length variation, uncertain ovulation timing, fertility treatments, and medical conditions can all influence the final clinical due date. Always prioritize medical guidance over online tools.
Quick guide to gestational age terms
- Gestational age: Age of pregnancy measured from LMP (not conception).
- Conception age (fetal age): Typically about 2 weeks less than gestational age.
- Term pregnancy: Often discussed in categories:
- Early term: 37w0d to 38w6d
- Full term: 39w0d to 40w6d
- Late term: 41w0d to 41w6d
- Post-term: 42w0d and beyond
Frequently asked questions
Can I use this if I only know my last period date?
Yes. If you know your LMP date, set the reference date to today and enter your current gestational age from your app or provider. A dedicated LMP-only calculator also works, but this one is best when gestational weeks are known.
What if I am carrying twins?
The biological due date math still starts with 40 weeks, but twin pregnancies are often managed with different delivery timing based on clinical factors. Use this estimate for orientation only and rely on your specialist's plan.
Can this calculator diagnose labor timing?
No. It cannot predict the exact day labor starts. It simply estimates the expected due date and major timeline points.
Bottom line
A due date calculator by weeks gestation is a practical way to convert “how far along” into a clear timeline. It can support planning, reduce confusion, and help you understand milestones. For official dating and pregnancy decisions, your healthcare provider remains the final authority.