Calculator Form
Example Data Table
| Method | Input Example | Reference Date | Sample Output Focus |
|---|---|---|---|
| LMP | LMP: 2026-01-01, Cycle: 28 days | 2026-03-17 | About 10 weeks pregnant, due near early October. |
| Conception Date | Conception: 2026-01-15 | 2026-03-17 | Due date estimated from 266 days after conception. |
| Known Due Date | Due Date: 2026-10-08 | 2026-03-17 | Weeks remaining count down directly from the due date. |
| Ultrasound Dating | Scan: 2026-02-20, GA: 8w 3d | 2026-03-17 | Pregnancy timeline reconstructed from scan age and scan date. |
Formula Used
Due Date = LMP + 280 days + (Cycle Length − 28 days)
Due Date = Conception Date + 266 days
Gestational Age in Days = 280 − (Due Date − Reference Date)
Estimated LMP = Ultrasound Date − Gestational Age at Scan
Weeks Remaining = (Due Date − Reference Date) ÷ 7
Pregnancy length is commonly estimated as 40 weeks from LMP or 38 weeks from conception. This tool converts those rules into day-based calculations for clearer tracking.
How to Use This Calculator
Choose the method that matches the information you already have. Enter your reference date, then complete the fields shown for that method.
Use the LMP option when you know the first day of your last menstrual period. Add your typical cycle length for a better estimate when your cycle differs from 28 days.
Use the conception option if you know the likely conception date. Use the due date option when your clinician has already given a confirmed due date.
Use the ultrasound option when you have a scan date and the gestational age reported on that scan. This is often helpful when menstrual dates are uncertain.
Click the calculate button. Review the due date, weeks remaining, current gestational age, trimester, milestone timing, and the Plotly timeline graph. Then export the result as CSV or PDF if needed.
FAQs
1. What does this calculator estimate?
It estimates the due date, current gestational age, weeks remaining, trimester, and milestone dates using LMP, conception, due date, or ultrasound inputs.
2. Which method is most commonly used?
LMP is the most common starting method. Ultrasound dating may be used when periods are irregular or cycle dates are uncertain.
3. Why does cycle length change the result?
A longer or shorter cycle can shift ovulation timing. That changes the estimated due date when the LMP method is used.
4. Can I use a future reference date?
Yes. A future reference date can help you estimate pregnancy week, trimester, and remaining time for appointments or planning.
5. What if the result says overdue?
That means your reference date is later than the estimated due date. It does not replace medical advice or delivery planning.
6. Is the due date exact?
No. Due dates are estimates. Actual delivery can happen earlier or later, and clinicians may revise dating after examination or ultrasound.
7. Why does fetal age differ from gestational age?
Gestational age counts from LMP. Fetal age is usually about two weeks less because conception happens after the cycle begins.
8. Should I rely on this instead of my doctor?
No. This tool is useful for planning and tracking, but your doctor or midwife should guide official pregnancy dating and care decisions.