Formula Used
LMP method: ECD = LMP + 280 days + cycle adjustment.
Cycle adjustment: cycle adjustment = average cycle length - 28.
Conception method: ECD = conception date + 266 days.
Ultrasound method: ECD = scan date + (280 - gestational age days).
Embryo transfer method: ECD = transfer date + (266 - embryo age days).
Gestational age: reference date - LMP equivalent date.
Example Data Table
| Method |
Main Input |
Extra Input |
Formula Rule |
Example Estimate |
| LMP |
January 1, 2026 |
28 day cycle |
Add 280 days |
October 8, 2026 |
| Conception |
January 15, 2026 |
None |
Add 266 days |
October 8, 2026 |
| Scan |
March 1, 2026 |
8 weeks, 3 days |
Add remaining days |
October 8, 2026 |
| Transfer |
January 20, 2026 |
Day 5 embryo |
Add 261 days |
October 8, 2026 |
How to Use This Calculator
- Select the method that matches your best available information.
- Enter the required date fields for that method.
- Adjust the cycle length when using the LMP method.
- Enter scan weeks and days when using ultrasound dating.
- Use the reference date to check current progress.
- Add notes when you want a clearer saved record.
- Press calculate to show the result above the form.
- Use CSV or PDF buttons to save your result.
Why Use This ECD Tool
An ECD calculator estimates an expected confinement date. Many people call it a due date. It gives a planning date, not a promise. Most births happen before or after the estimate. A clear calculator helps compare common dating methods in one place.
What This Calculator Checks
This tool supports several inputs. You can use the first day of the last menstrual period. You can adjust the average cycle length. You can also use a known conception date. Scan dating is available when gestational age was measured on a specific day. Assisted treatment users can choose a three day or five day embryo transfer.
Why Methods Can Differ
Each method starts from a different known point. LMP dating assumes ovulation near day fourteen in a twenty eight day cycle. Cycle adjustment moves the estimate when ovulation likely happened earlier or later. Conception dating starts closer to fertilization. Ultrasound dating uses measured fetal growth. Transfer dating uses embryo age and transfer timing.
Reading The Result
The main result is the estimated date. The calculator also shows days remaining, completed weeks, trimester, and milestone dates. These extra values help with calendars, appointments, travel planning, and general preparation. They also make it easier to compare two estimates from different records.
Practical Planning
Use the estimate as a guide. Keep notes about the source used. A scan from early pregnancy may differ from an LMP date. A clinician may prefer one method based on timing and reliability. The calculator stores nothing on the server. Your result is created during the page request. You can export the visible result as a CSV file or a simple PDF summary.
Limits To Remember
ECD calculations do not replace medical advice. They cannot predict labor, complications, or individual progress. Irregular cycles, uncertain dates, late scans, and health factors may change interpretation. Always confirm important decisions with a qualified professional. Use this page for organized planning, quick comparisons, and record keeping.
Best Records To Keep
Save the method, input date, cycle length, and export time. Note any scan age used. This record helps you explain the calculation later. It also helps compare updates after appointments, especially when different notes show different estimates during ongoing planning.
FAQs
What does ECD mean?
ECD usually means estimated confinement date. It is commonly used as another term for an estimated due date. It is a planning estimate, not a guaranteed birth date.
Which method should I choose?
Choose the method based on your best known date. Use LMP for cycle records. Use conception for a known conception date. Use scan dating when a medical scan measured gestational age.
Why does cycle length matter?
The standard LMP method assumes a 28 day cycle. Longer or shorter cycles can shift likely ovulation. The calculator adjusts the estimated date using that difference.
Can this predict the exact delivery date?
No. It estimates a date from common calendar rules. Actual delivery can happen earlier or later. Always use professional guidance for medical decisions.
How is ultrasound dating calculated?
The calculator subtracts the measured gestational age from 280 days. It then adds the remaining days to the scan date to estimate ECD.
How is embryo transfer dating handled?
The calculator uses the transfer date and embryo age. A day 3 embryo adds 263 days. A day 5 embryo adds 261 days.
What is the reference date?
The reference date checks progress on a chosen day. It helps calculate gestational age, trimester estimate, and days remaining from that specific date.
Can I save my result?
Yes. After calculation, use the CSV button for spreadsheet records. Use the PDF button for a simple printable summary of the visible result.