Calculator Input
Example Data Table
| Method | Input Dates | Cycle | Estimated Ovulation | Fertile Window | Estimated Due Date |
|---|---|---|---|---|---|
| LMP | LMP: January 3, 2026 | 28-day cycle, 14-day luteal | January 17, 2026 | January 12 to January 18, 2026 | October 10, 2026 |
| Ovulation | Ovulation: February 20, 2026 | 30-day cycle, 14-day luteal | February 20, 2026 | February 15 to February 21, 2026 | November 13, 2026 |
| Conception | Conception: March 5, 2026 | 27-day cycle, 13-day luteal | March 5, 2026 | February 28 to March 6, 2026 | November 26, 2026 |
Formula Used
1) LMP method: Estimated due date = LMP + 280 days.
2) Ovulation method: Estimated due date = Ovulation date + 266 days.
3) Conception method: Estimated due date = Conception date + 266 days.
4) Ovulation from cycle: Ovulation date = LMP + (Cycle length - Luteal phase).
5) Fertile window: Fertile start = Ovulation - 5 days; Fertile end = Ovulation + 1 day.
6) Gestational age today: Days since LMP, displayed as weeks and days.
How to Use This Calculator
- Select the method that best matches your information.
- Enter the first day of your last period, or a known ovulation or conception date.
- Adjust cycle length and luteal phase for a more tailored estimate.
- Click Calculate Timing to show results above the form.
- Review ovulation, conception, fertile days, implantation window, and due date.
- Use the chart for a visual timeline of key pregnancy milestones.
- Download a CSV or PDF copy for records or discussion.
- Compare the estimate with clinical advice when dates are uncertain.
Frequently Asked Questions
1) Which method is best?
Use a known ovulation or conception date when it is reliable. Use the LMP method when period timing is clear. Ultrasound can refine dates when cycle timing is uncertain.
2) Why does the calculator ask for cycle length?
Cycle length helps estimate ovulation when only the last period date is known. A longer or shorter cycle can shift expected ovulation and fertile days.
3) What is the luteal phase?
The luteal phase is the time between ovulation and the next period. It is often near 14 days, but some people have shorter or longer luteal phases.
4) Is ovulation always the conception date?
Not exactly. Conception often happens near ovulation, but timing can vary slightly. This tool uses ovulation and conception as close practical estimates.
5) Why can ultrasound change the due date?
Ultrasound uses fetal size and developmental timing. It can offer a more consistent estimate when the last period date is uncertain or cycles are irregular.
6) Does this tool diagnose pregnancy problems?
No. It gives timing estimates only. It cannot confirm pregnancy health, implantation success, or exact delivery date. Clinical review is still important.
7) Why is the fertile window wider than one day?
Sperm can survive for several days, while the egg is available for a shorter time. That is why the fertile range extends before and slightly after ovulation.
8) Can irregular cycles reduce accuracy?
Yes. Irregular cycles can shift ovulation timing, which changes fertile days and due date estimates. Known ovulation dates or ultrasound review usually improve accuracy.