Pregnancy Due Date Calculator Calculators
Estimate a due date and see the current stage of pregnancy.
Pregnancy Due Date Calculator is a free online tool that estimate a due date and see the current stage of pregnancy. It runs entirely in your web browser using plain JavaScript, so files are processed on your own device and never uploaded to a server. There is no sign-up, no file size limit imposed by the site, no watermark and no paid tier.
- Price
- Free — no account, no quota, no watermark
- Category
- Calculators
- Where it runs
- In your browser, on your device
- Files uploaded
- None
- Technology
- plain JavaScript
- Settings
- 2
- Works offline
- Yes, after the first visit
About Pregnancy Due Date Calculator
Naegele's rule adds 280 days to the first day of the last period, adjusted here for cycles that are not 28 days. It is an estimate and a fairly rough one — fewer than 5% of babies arrive on the estimated date, and a dating scan in the first trimester is considerably more accurate.
How to use it
- Enter first day of last period and average cycle length (days).
- Results update the moment anything changes.
The 2 settings
| Setting | What it does | Default |
|---|---|---|
| First day of last period | Free text. | — |
| Average cycle length (days) | Range 20–45. | 28 |
Under the hood
| Runs on | plain JavaScript — runs the whole thing |
| Controls | First day of last period, Average cycle length (days) |
Questions
How accurate is this?
About 80% of births happen within two weeks either side of the estimate. If your cycles are irregular or you are unsure of dates, only a scan can date the pregnancy reliably. This is not medical advice.
What are the limits on average cycle length (days)?
It accepts 20 to 45, starting at 28.
Is the arithmetic exact?
It uses double-precision floating point — about 15 significant figures, far more than the inputs justify. Displayed rounding is cosmetic; the underlying numbers are not rounded between steps, so chained results do not drift.