How to use Pregnancy Week
Estimate gestational weeks and days from a due date.
- Choose the operation and enter every labeled input, keeping units and the time period consistent.
- Calculate, compare the worked example below and inspect any warnings.
- Change one assumption to compare another scenario; keep the model’s limits in view.
Formula & calculation method
Estimated start = supplied due date − 280 days. Gestational days = reference date − estimated start. Divide by seven to express completed weeks and remaining days.
Input reference · 2 fields
These labels describe the calculation’s base units. Supported measurements can switch through the header’s region settings; follow the current workspace labels. Prefilled values are examples.
- Estimated due date
- Use a valid calendar date; dates carry no time zone.
- Reference date
- Use a valid calendar date; dates carry no time zone.
A quick example
Exactly 140 days before the due date corresponds to 20 weeks.
Assumptions, edge cases & limits
- The supported reference date runs from the estimated start through 44 weeks.
- Gestational age is not the same as time since conception and does not assess pregnancy health.
- Uses the due date you provide; it does not establish or revise clinical pregnancy dating.
Questions about Pregnancy Week
What does 12 weeks and 3 days mean?
It means 12 completed seven-day weeks plus three further days under the due-date assumption you entered. It is a dating calculation, not an assessment of development or wellbeing.
Which due date should I enter if my dates changed?
Use the latest due date your maternity team has advised. The calculator cannot determine whether a revised due date is clinically appropriate.
Are my files or inputs uploaded?
Calculation and file processing run in your browser without a processing upload. Downloads go to your device. Choosing a next-step transfer creates a temporary local copy for that workflow. Region preferences are stored separately from tool inputs. See our privacy details.
Can I use this tool for free?
Yes. No signup, subscription or payment is required to use the tool or download its output. File tools have device and size limits; a smaller batch may work better on a phone.
Method & references
Read the underlying method or measurement convention in context. These references do not imply affiliation or endorsement.
ACOG: Methods for estimating the due date ↗NHS: Due date calculator ↗Educational health estimates. No independent clinical review is claimed.A result or explanation needs correcting? Tell us the tool name and an example.