Calculator Input
Select one dating method, enter the related values, and submit to generate estimated pregnancy dates and milestones.
Example Data Table
| Method | Example Inputs | Estimated Due Date | Notes |
|---|---|---|---|
| Last Menstrual Period | LMP: January 1, 2026; cycle length: 28 days | October 8, 2026 | Standard 280-day estimate from LMP. |
| Conception Date | Conception: January 15, 2026 | October 8, 2026 | Add 266 days from conception. |
| IVF Transfer Date | Transfer: January 20, 2026; embryo age: 5 days | October 8, 2026 | Adjust for embryo age at transfer. |
| Ultrasound Dating | Scan: March 4, 2026; gestational age: 9 weeks 0 days | October 7, 2026 | Subtract measured gestational age from 280 days. |
Formula Used
1. Last Menstrual Period method: Estimated due date = LMP + 280 days + (cycle length - 28 days).
2. Conception method: Estimated due date = conception date + 266 days.
3. IVF method: Estimated due date = transfer date + (266 - embryo age in days).
4. Ultrasound method: Estimated due date = ultrasound date + (280 - gestational age in days at scan).
Milestones: Trimester changes and term windows are counted from the estimated LMP date using gestational age in days.
How to Use This Calculator
- Choose the dating method that best matches your available information.
- Enter the related date fields and any required supporting values.
- Click Calculate Due Date to generate the estimate.
- Review the due date, gestational age, trimester timing, and milestone dates.
- Use the export buttons to save the results as CSV or PDF.
- Compare your estimate with professional prenatal guidance when needed.
FAQs
1. How accurate is a pregnancy due date estimate?
A due date is an estimate, not an exact delivery prediction. Many pregnancies deliver before or after the calculated date. Early ultrasound often improves dating accuracy.
2. Why does cycle length change the LMP result?
Ovulation often shifts with longer or shorter cycles. Adjusting the cycle length can better match the likely ovulation date and improve the estimated due date.
3. Why can ultrasound change the estimated date?
Ultrasound estimates fetal size and gestational age. If the scan suggests different timing than LMP, clinicians may revise the due date, especially earlier in pregnancy.
4. Is IVF dating usually more precise?
Yes. IVF uses a known transfer date and embryo age, so pregnancy dating is usually more precise than methods based only on cycle history.
5. Is the conception date exact?
Not always. Conception may not be known exactly unless timed medical treatment or fertility tracking identifies it clearly. Natural conception estimates can still vary by a few days.
6. What if my due date has already passed?
The calculator will show how many days you are past the estimate. Contact your maternity care team for guidance, monitoring, and next-step recommendations.
7. Does every pregnancy last exactly 280 days?
No. Two hundred eighty days is a standard reference from LMP. Actual delivery timing varies with cycle length, ovulation timing, and individual pregnancy factors.
8. Should this calculator replace medical advice?
No. This tool helps with planning and understanding dates. Medical decisions, redating, and pregnancy concerns should always be discussed with a qualified clinician.