Calculator
Example Data Table
| Method | Input Example | Formula Basis | Projected Due Date |
|---|---|---|---|
| Last Period | LMP: January 1, 2026 | LMP + 280 days | October 8, 2026 |
| Conception | Conception: January 15, 2026 | Conception + 266 days | October 8, 2026 |
| Ultrasound | March 1, 2026 at 8w 0d | Scan date + remaining gestation | October 11, 2026 |
| IVF | Day 5 transfer: January 20, 2026 | Transfer + 261 days | October 8, 2026 |
Formula Used
The calculator uses standard pregnancy dating formulas. For last menstrual period dating, the base estimate is LMP + 280 days. This equals 40 weeks of gestation. If the cycle is longer or shorter than 28 days, the calculator adjusts the estimate by the cycle difference.
For conception dating, the formula is conception date + 266 days. For ultrasound dating, the formula is scan date + (280 − gestational age in days). For IVF dating, the formula is transfer date + (266 − embryo age in days).
How to Use This Calculator
- Select the dating method that matches your available information.
- Enter the required date fields for that method.
- Add cycle length, scan age, or embryo transfer type when needed.
- Choose whether to display pregnancy milestones.
- Press the calculate button to view the result above the form.
- Use CSV or PDF buttons to save the calculated summary.
Understanding Projected Due Dates
Why Due Dates Are Estimates
A projected due date is a planning estimate. It is not a guaranteed birth date. Pregnancy length can vary from person to person. Many babies arrive before or after the calculated date. The estimate still helps with appointments, testing windows, leave planning, and personal preparation.
Choosing the Right Input Method
The last menstrual period method is common. It works best when cycles are regular. It assumes ovulation near day fourteen of a twenty-eight day cycle. A longer cycle often moves the due date later. A shorter cycle may move it earlier.
When Conception or IVF Dates Help
A known conception date can improve the estimate. This is useful when tracking ovulation closely. IVF dating can be even more specific because the embryo age and transfer date are known. The calculator subtracts the embryo age from the standard conception-based pregnancy length.
Using Ultrasound Dating
Ultrasound dating uses the measured gestational age on the scan date. Early scans are often used to confirm pregnancy timing. Later scans may show growth differences, so they may not always replace earlier dating. Your clinician may choose the most reliable date.
Reading the Result
The result shows the projected due date, estimated conception date, gestational age, trimester, and days remaining. Optional milestones can show useful planning points. These dates can support organization, but they should not replace medical guidance.
FAQs
1. What is a projected due date?
A projected due date is an estimated delivery date based on pregnancy dating inputs. It helps with planning but does not guarantee the actual birth date.
2. Which method is most accurate?
Early ultrasound and IVF dating can be more specific. LMP dating works well when cycles are regular and the period date is known.
3. Why does cycle length matter?
Cycle length affects the likely ovulation date. Longer cycles may delay conception timing, while shorter cycles may move it earlier.
4. Can this calculator replace medical advice?
No. This tool provides an estimate only. A qualified healthcare provider should confirm pregnancy dating and clinical decisions.
5. How is IVF due date calculated?
IVF dating uses the embryo transfer date and embryo age. The calculator adds the remaining days from conception-based pregnancy length.
6. Why is conception date different from LMP?
Gestational age usually starts from the last period. Conception commonly happens about two weeks after that starting point.
7. Are milestone dates exact?
Milestone dates are planning estimates. Appointment timing can vary by provider, pregnancy history, local practice, and medical needs.
8. Can I download my results?
Yes. After calculation, use the CSV or PDF button above the form to save a copy of your estimated dates.