Pregnancy Due Date Calculator
Estimate your baby's due date from the first day of your last period or from a known conception date. See how many weeks along you are, your current trimester, and the key milestone dates — all worked out instantly in your browser.
Enter a date above to estimate your due date.
Estimated due date
—
| Milestone | Date |
|---|
This is an estimate for general information only and is not medical advice. Your input stays in your browser — nothing is sent anywhere.
How the due date calculator works
The most common way to estimate a due date is Naegele's rule: take the first day of your last menstrual period (LMP) and add 280 days — that is 40 weeks. This works because pregnancy is conventionally dated from the LMP rather than from conception, and the typical span from LMP to birth is about 40 weeks.
Naegele's rule assumes a regular 28-day cycle with ovulation around day 14. If your cycles are longer or shorter, you ovulate — and conceive — later or earlier, so this calculator shifts your due date by the difference. Enter your average cycle length to fine-tune the estimate. If you instead know your conception or ovulation date, switch the method above and the tool adds 266 days (38 weeks) to that date.
Gestational age — how far along you are — is shown in completed weeks plus extra days, like 12w 3d. Because the clock starts at the LMP, you are counted as roughly two weeks along at the moment of conception. The milestone table marks the end of each trimester, the start of full term at 37 weeks, and the estimated due date at 40 weeks.
Everything runs in your browser — the dates you enter are never uploaded or stored.
Common questions
Will my baby arrive on the due date? Probably not exactly. The due date is a single best-guess day, but only about 1 in 20 babies are born on it. A normal full-term birth can happen any time between 37 and 42 weeks.
Which date is most accurate? An early ultrasound dating scan is usually the most reliable, especially if your cycles are irregular or you are unsure of your last period. Always go by the due date your doctor or midwife gives you.
My cycle is not 28 days — does that matter? Yes, a little. A longer cycle pushes ovulation later, so the due date moves back; a shorter cycle moves it earlier. Set your average cycle length above to account for this.
Is anything saved or uploaded? No. The tool is fully client-side — your dates never leave your browser and nothing is stored.
This calculator is for general information and planning only. It is not a substitute for professional medical advice, diagnosis, or care.