Enter pregnancy dating inputs
Example data table
| LMP Date | Cycle Length | Reference Date | Estimated Due Date | Estimated Conception Date | Gestational Age |
|---|---|---|---|---|---|
| 2026-01-01 | 28 days | 2026-03-12 | October 8, 2026 | January 15, 2026 | 10 weeks, 0 days |
Formula used
Base due date formula: Estimated Due Date = LMP + 280 days.
Cycle-adjusted formula: Estimated Due Date = LMP + 280 days + (Cycle Length − 28 days).
Estimated conception formula: Conception Date ≈ LMP + (Cycle Length − 14 days).
Gestational age formula: Gestational Age = Reference Date − Dating Anchor, shown in weeks and days.
Ultrasound comparison formula: Ultrasound Due Date = Ultrasound Date + (280 − Ultrasound Gestational Age in days).
How to use this calculator
- Enter the first day of the last menstrual period.
- Add the average cycle length if it differs from 28 days.
- Choose a reference date to see gestational age on that day.
- Optionally enter ultrasound details to compare two dating estimates.
- Click Calculate Due Date to show results above the form.
- Review the due date, conception estimate, trimester dates, and term milestones.
- Use the CSV or PDF buttons to keep a shareable record.
- Discuss any discrepancy with a qualified clinician before using the dates clinically.
Frequently asked questions
1. What does LMP mean?
LMP means the first day of the last menstrual period before pregnancy. It is a standard starting point for estimating gestational age and an expected due date.
2. Why does the calculator ask for cycle length?
Cycle length can shift the likely ovulation date. Longer cycles may push the due date later, while shorter cycles may pull the estimate earlier.
3. Is the due date exact?
No. It is an estimate used for planning and review. Many births occur before or after the projected date.
4. Why include a reference date?
The reference date lets you calculate gestational age for today, a clinic visit, or any planned review point without changing the main due date estimate.
5. What is the ultrasound comparison for?
It helps compare the LMP estimate with a scan-based estimate. A clinician may use scan information to confirm or revise dating when dates do not align.
6. Can I use this for irregular cycles?
You can use it for a rough estimate, but irregular cycles reduce certainty. Ultrasound dating and clinical assessment are more reliable when cycles vary widely.
7. Does this calculator diagnose pregnancy problems?
No. It only estimates dates and gestational timing. It does not diagnose miscarriage, ectopic pregnancy, growth concerns, or labor timing.
8. When should I contact a clinician?
Contact a clinician for pain, bleeding, uncertain dates, very irregular cycles, or any major difference between menstrual history and ultrasound findings.