Pregnancy Week Calculator

Calculate Pregnancy Week

Choose the date method you know best, then review the due date, trimester, milestones, and timeline progress.

Calculation method

Use the most reliable date available.

Current date

Results are measured against this date.

Last menstrual period date

Used as day 0 of pregnancy dating.

Average cycle length

A longer cycle may shift ovulation later.

Conception date

Usually about two weeks after LMP.

Known due date

Useful when a due date is already confirmed.

Embryo transfer date

Use the actual transfer date from treatment.

Embryo age at transfer

This affects the due date calculation.

Optional adjustment from scan

Enter days to shift the full timeline forward or backward.

Example Data Table

This sample shows how one set of dates can map to a current pregnancy week, trimester, and estimated due date.

Method	Reference Date	Cycle Length	Current Date	Pregnancy Week	Gestational Age	Trimester	Estimated Due Date
Last menstrual period	Jan 01, 2026	28 days	Mar 31, 2026	Week 13	12 weeks 5 days	First trimester	Oct 08, 2026

Formula Used

The calculator converts the chosen reference date into a gestational timeline, then measures progress against a standard 40-week pregnancy.

LMP method: Due date = LMP + 280 days + (cycle length - 28).
Conception method: Due date = conception date + 266 days.
Due date method: Estimated LMP = due date - 280 days.
IVF method: Estimated conception date = transfer date - embryo age in days.
Gestational age: Current date - estimated LMP = total pregnancy days completed.
Pregnancy week: Completed weeks = floor(total days / 7), then the current week is completed weeks + 1.
Timeline progress: Progress % = (gestational days / 280) × 100, capped between 0 and 100.
Adjustment field: Any entered day shift moves the full timeline, including conception, due date, and milestones.

How to Use This Calculator

Use the most reliable date you know, then review the timeline, due date, and milestone dates generated from that input.

Select the calculation method that best matches the information you have.
Enter your LMP, conception date, due date, or embryo transfer date.
Add cycle length only when you use the LMP method.
Choose the current date you want to measure the pregnancy against.
Apply an optional scan-based day adjustment when you want to compare another dating estimate.
Click the calculate button to view the pregnancy week, gestational age, due date, and milestone schedule.
Use the CSV or PDF buttons after calculation to save or share the report.

Important: This tool is for planning and estimation. It does not replace prenatal care, ultrasound interpretation, or medical advice from a qualified clinician.

FAQs

These answers explain the most common pregnancy week calculation questions in plain language.

1. How is pregnancy week calculated?

This calculator converts your chosen reference date into a gestational timeline. LMP starts at day 0, conception adds 266 days to reach due date, and due-date mode back-calculates 280 days to estimated LMP.

2. Why does cycle length matter?

Ovulation often shifts with cycle length. A longer cycle can move estimated conception and due date slightly later, while a shorter cycle may move them earlier. This matters most with the LMP method.

3. Which method is usually most accurate?

Use the best date you know. Reliable IVF transfer dates are often strongest, conception dates can be helpful, and LMP works well when periods are regular. Clinical ultrasound can refine dating.

4. Can this replace medical advice?

No. It provides an estimate for planning and education. Prenatal visits, ultrasound findings, symptoms, and clinician guidance should shape health decisions, especially when cycles are irregular or dates are uncertain.

5. What if I am already past 40 weeks?

The calculator will still show your gestational age and overdue days. Many pregnancies continue beyond 40 weeks, but monitoring plans differ, so follow your clinician’s advice for timing and testing.

6. Why can LMP and conception methods differ?

They begin from different anchors. LMP counts pregnancy from the first day of the last period, while conception starts about two weeks later. Date uncertainty and cycle variation can also shift the estimate.

7. What does the optional adjustment field do?

It shifts the estimated timeline forward or backward by the number of days entered. Use it when you want to compare your own estimate with another dating adjustment, such as an ultrasound-based revision.

8. Can I export my result?

Yes. After calculating, use the CSV button for spreadsheet review or the PDF button for a shareable snapshot. The export includes key results and milestone dates shown in the report area.