Calculator
Example Data Table
| Method | Input Date | Cycle Length | Current Date | Estimated Week | Estimated Due Date |
|---|---|---|---|---|---|
| Last menstrual period | 2026-01-01 | 28 | 2026-03-20 | Week 12, Day 2 | 2026-10-08 |
| Conception date | 2026-01-15 | Not used | 2026-03-20 | Week 12, Day 2 | 2026-10-08 |
| Known due date | 2026-10-08 | Not used | 2026-03-20 | Week 12, Day 2 | 2026-10-08 |
Formula Used
LMP method: gestational age in days = (current date − LMP date) + (cycle length − 28).
LMP due date: due date = LMP date + 280 days + (cycle length − 28).
Conception method: gestational age in days = (current date − conception date) + 14.
Conception due date: due date = conception date + 266 days.
Known due date method: gestational age in days = 280 − (due date − current date).
Week number: pregnancy week = floor(gestational age in days ÷ 7) + 1.
Progress: progress percentage = gestational age in days ÷ 280 × 100.
How to Use This Calculator
- Select whether you want to calculate from the last period, conception date, or a known due date.
- Enter the current date so the calculator can work out the present gestational age accurately.
- If using the last period method, add your usual cycle length to improve date matching for shorter or longer cycles.
- Click the calculate button to show the result directly below the header and above the form.
- Review the week guide, trimester status, progress chart, milestone dates, and screening window table.
- Use the CSV or PDF buttons to save the current result for planning discussions or personal records.
Important Note
This tool is educational and planning-focused. It cannot diagnose pregnancy health, replace ultrasound dating, or substitute for urgent advice from a qualified clinician.
FAQs
1. Which method should I use?
Use the last menstrual period if you know that date well. Use conception date if ovulation or fertility treatment timing is known. Use a known due date if your clinician has already confirmed it.
2. Why does cycle length matter?
Standard dating assumes a 28-day cycle. A longer or shorter cycle can shift ovulation timing, so the calculator adjusts the estimated gestational age and due date to match that average pattern.
3. Is the due date exact?
No. It is an estimate used for planning, monitoring, and discussion. Actual birth can happen before or after that date, especially when cycles are irregular or dating information is incomplete.
4. Why might ultrasound dating differ?
Ultrasound can refine dating, especially in early pregnancy, because fetal measurements may better reflect actual gestational age when the last period is uncertain or cycles vary a lot.
5. Does this calculator work for twins?
It can still estimate week and due date structure, but multiple pregnancies often need individualized monitoring, scan timing, and visit frequency. Always follow your own clinician’s schedule.
6. Why are some screening windows marked as current?
The calculator compares your present week with broad timing ranges for common pregnancy checks. A current label means the timing overlaps your week, not that you personally need the test.
7. What if my result shows overdue days?
That means the current date is later than the estimated due date. It does not describe your baby’s condition. It simply flags that the pregnancy is beyond the estimated forty-week point.
8. Can I save the result?
Yes. Use the CSV button for spreadsheet-friendly data or the PDF button for a printable summary. The exported file reflects the result currently displayed on the page.