Calculator Inputs
Use the method you trust most. The result appears above this form after calculation.
Example data table
| Method | LMP | Cycle Length | As Of | Gestational Age | Due Date | Trimester |
|---|---|---|---|---|---|---|
| Last menstrual period | 2026-01-15 | 28 days | 2026-03-19 | 9 weeks 0 days | 2026-10-22 | First |
| Conception date | Calculated | Not needed | 2026-03-19 | Depends on entered conception date | Conception + 266 days | Auto-mapped |
Formula used
1. Due date from LMP: Estimated due date = LMP + 280 days + (cycle length - 28 days).
2. Due date from conception: Estimated due date = conception date + 266 days.
3. LMP from due date: LMP = due date - 280 days.
4. Ultrasound dating: LMP = ultrasound date - stated gestational age at scan.
5. Gestational age: Gestational days = as of date - LMP date. Displayed age = completed weeks + remaining days.
6. Current chart week: Current week = floor(gestational days ÷ 7) + 1.
7. Trimester ranges: Weeks 1 to 13 are first, 14 to 27 are second, and 28 onward are third trimester.
How to use this calculator
- Select the dating method you have available.
- Enter your most reliable date or scan information.
- Set the “as of” date for the timeline check.
- Choose how far the week chart should extend.
- Press Calculate Pregnancy Chart.
- Review the result panel above the form.
- Study the week chart, milestone notes, and graph.
- Download the timeline as CSV or PDF if needed.
FAQs
1. What does this pregnancy week chart calculator show?
It shows gestational age, current chart week, due date, trimester, approximate month, milestone dates, and a full week-by-week pregnancy timeline for planning and tracking.
2. Which input method is usually best?
Use the most reliable source you have. Early ultrasound dating is often very helpful, while LMP works best when cycles are regular and the starting date is known.
3. Why can cycle length change the due date?
People with longer or shorter cycles may ovulate earlier or later than day 14. Adjusting the cycle length can shift the estimated due date when using LMP.
4. Why are pregnancy weeks and months different?
Pregnancy dating is traditionally measured in weeks because it is more precise. Months are approximate groupings and do not map evenly across every calendar month.
5. Does this calculator predict the exact birth date?
No. It estimates timing using standard clinical rules. Many births happen before or after the estimated due date, so the result is a planning guide.
6. What is considered full term?
Pregnancy is commonly described as early term from 37 weeks, with 39 weeks often treated as a key full-term benchmark for many planning discussions.
7. Can I use ultrasound dating later in pregnancy?
You can, but earlier scans are generally more precise for dating. Later scans help with monitoring growth and position but may be less exact for setting dates.
8. Is this tool medical advice?
No. It is an educational calculator. Please contact a qualified clinician for symptoms, bleeding, severe pain, reduced movement, or any urgent pregnancy concern.