Due Date Calculator
From your last menstrual period, get your due date, gestational age, and ovulation and fertile window at once (for reference)
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Enter the first day of your last menstrual period (LMP) and your average cycle length, and this tool uses Naegele's rule to calculate your due date, current gestational age, and estimated ovulation date and fertile window all at once. It's a reference tool for those trying to conceive or already pregnant to gauge a rough timeline, and all calculations happen only within your browser.
How to use
- Select the first day of your last menstrual period (LMP) as a date.
- The reference date is prefilled with today's date by default and can be changed to any date you like.
- Enter your average cycle length (28 days by default) to match your own cycle, and the due date and ovulation date are adjusted accordingly.
- Check your due date, current gestational age, ovulation and fertile window, and days remaining, then copy the results.
FAQ
- How is the due date calculated?
- Following Naegele's rule, it adds 280 days (40 weeks) to the first day of your last period. If your cycle isn't 28 days, the due date is adjusted by that difference. Actual delivery dates vary widely, within about two weeks before or after the due date.
- Are the estimated ovulation date and fertile window accurate?
- The estimated ovulation date is calculated as roughly 14 days before your next expected period, and the fertile window is shown as 5 days before ovulation through 1 day after. Actual ovulation varies with your condition and cycle fluctuations, so use this for reference only.
- Are the dates I enter sent to a server?
- No. All calculations happen only within your browser, and no inputs such as your last period date or cycle length are ever transmitted to or stored on a server. For an accurate diagnosis, see an OB-GYN (this is for reference and may differ from reality).