EDC Calculator (By LMP)
Use your last menstrual period (LMP) and average cycle length to estimate your expected date of confinement (EDC), also called your estimated due date.
What does “EDC by LMP” mean?
EDC stands for Expected Date of Confinement, a traditional medical term for your estimated due date. “By LMP” means the estimate is based on the first day of your last menstrual period. This is one of the most common starting points in obstetric care because it is easy to report and works well for many people with regular cycles.
If you searched for a pregnancy due date calculator, gestational age calculator, or LMP due date calculator, you are in exactly the right place. This tool gives you a fast estimate and helps you understand where you are in pregnancy right now.
How this EDC calculator works
This calculator uses the standard Naegele-style dating approach:
- Start with the first day of your LMP.
- Add 280 days (40 weeks) for a 28-day cycle.
- Adjust by cycle length difference if your average cycle is shorter or longer than 28 days.
For example, if your cycle is 30 days, the estimate is shifted 2 days later. If your cycle is 26 days, the estimate is shifted 2 days earlier.
How to use the calculator
Step 1: Enter your LMP date
Choose the first day bleeding started in your last menstrual period. This is not ovulation day and not implantation day.
Step 2: Enter cycle length
Use your typical cycle length based on the last several months. If you are unsure, leave it at 28 days.
Step 3: Review your results
You’ll get:
- Your estimated due date (EDC)
- Your estimated gestational age today
- Current trimester and days remaining
- A practical “full-term window” around the due date
Why your due date is an estimate
Only a small percentage of births happen on the exact due date. Most healthy pregnancies deliver within a range around that date. The EDC is best used as a planning anchor for prenatal visits, testing milestones, and preparation.
Dating accuracy may be affected by:
- Irregular menstrual cycles
- Recent hormonal contraception changes
- Breastfeeding with delayed ovulation return
- Uncertain LMP date
- Late or early ovulation compared with average
When ultrasound may change your date
In clinical care, first-trimester ultrasound can refine dating, especially if LMP is uncertain or cycles are irregular. Your provider may adjust your estimated due date if ultrasound measurements differ significantly from the LMP-based estimate.
This is normal and helps improve accuracy for prenatal care timing.
Practical planning checklist after you calculate EDC
- Book or confirm your first prenatal appointment.
- Start (or continue) prenatal vitamins with folic acid as advised.
- Track symptoms, medications, and questions for your provider.
- Plan key windows: anatomy scan, glucose screening, and birth classes.
- Review nutrition, hydration, sleep, and activity goals.
Quick FAQ
Is EDC the same as due date?
Yes. EDC is the medical shorthand for your estimated due date.
What if I do not remember my exact LMP?
Use your best estimate and discuss it at your appointment. Ultrasound can help establish more accurate dating.
Can cycle length really change the date?
Yes. A longer or shorter cycle can shift expected ovulation and therefore shift the estimated due date.
Does this replace medical advice?
No. This tool is educational and planning-oriented. Your care team should make final clinical decisions.
Bottom line
An EDC calculator by LMP is a simple, useful first step for understanding pregnancy timing. Use it for orientation, planning, and informed conversations with your clinician. For the best accuracy, combine LMP dating with professional prenatal care and recommended imaging when appropriate.