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Health & Fitness

Pregnancy Due Date & Ovulation Calculator

Estimate your due date from your last period or conception date, or find your estimated ovulation day and fertile window — all calculated instantly in your browser.

What this does: estimates your pregnancy due date using standard date-based formulas (last menstrual period + 280 days, adjusted for cycle length, or conception date + 266 days), plus a simple ovulation and fertile-window estimate. Everything runs locally in your browser — this is sensitive health data, and nothing you enter is ever transmitted, uploaded, or stored anywhere.

Estimates only, not medical advice — actual dates vary from person to person. Consult your healthcare provider for a confirmed due date and pregnancy dating. This is sensitive health information: nothing you type here is sent anywhere; all calculations stay in your browser.

Frequently asked questions

How is the pregnancy due date calculated?

The most common method (Naegele's rule) adds 280 days to the first day of your last menstrual period (LMP), assuming a 28-day cycle. This tool adjusts that estimate for your actual average cycle length. If you know your conception date instead, the due date is estimated as 266 days after conception. Either way, the result is an estimate: only about 5% of babies arrive on the exact predicted date.

How is ovulation day and the fertile window estimated?

Ovulation is estimated to occur roughly 14 days before your next period starts, so the tool calculates it as your last period's start date plus (cycle length minus 14) days. The fertile window shown is that estimated ovulation day, plus or minus 5 days, covering the days when conception is most possible. Actual ovulation timing varies and can shift cycle to cycle.

Is this calculator a substitute for medical advice?

No. This tool provides estimates only, based on standard date-arithmetic formulas used as a general starting point. It is not a diagnosis and does not replace an ultrasound-confirmed due date or guidance from a healthcare provider. All calculations run locally in your browser; nothing you enter is transmitted or stored anywhere.