Naegele's rule: due date = first day of last period + 280 days, adjusted for cycles longer or shorter than 28 days. Only about 1 in 25 babies arrive on the due date itself.
| Milestone | Date |
|---|---|
| End of first trimester (12 weeks) | Tue, 2 Jun 2026 |
| NT scan window (11–14 weeks) | Tue, 26 May 2026 |
| Anomaly scan (18–20 weeks) | Tue, 14 Jul 2026 |
| Second trimester ends (27 weeks) | Tue, 15 Sep 2026 |
| Glucose test (24–28 weeks) | Tue, 25 Aug 2026 |
| Full term begins (37 weeks) | Tue, 24 Nov 2026 |
| Due date (40 weeks) | Tue, 15 Dec 2026 |
| 42 weeks (overdue) | Tue, 29 Dec 2026 |
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Your estimated due date is the date your pregnancy reaches 40 weeks, counted from the first day of your last menstrual period (LMP) rather than from conception. This calculator uses Naegele's rule, the method doctors have used since 1812 and still use today.
Enter the first day of your last period and your average cycle length to see your due date, roughly when you conceived, and how far along you are right now.
| First Day of Last Menstrual Period | 10 Mar 2026 |
| Average Cycle Length | 28 days |
| Estimated due date | Tue, 15 Dec 2026 |
| Likely delivery window (37–42 weeks) | 24 Nov – 29 Dec 2026 |
| Estimated conception date | Tue, 24 Mar 2026 |
| How far along today | 32 weeks 2 days (third trimester) |
| Days to go | 54 days |
| Zodiac sign of a baby born on the due date | Sagittarius |
Due date Tue, 15 Dec 2026; conceived around Tue, 24 Mar 2026.
Try this example →| First Day of Last Menstrual Period | 1 Jan 2026 |
| Average Cycle Length | 35 days |
| Estimated due date | Thu, 15 Oct 2026 |
| Likely delivery window (37–42 weeks) | 24 Sep – 29 Oct 2026 |
| Estimated conception date | Thu, 22 Jan 2026 |
| How far along today | 41 weeks 0 days (third trimester) |
| Days to go | 0 days |
| Zodiac sign of a baby born on the due date | Libra |
Due date Thu, 15 Oct 2026.
Try this example →Naegele's rule is accurate to within about 2 weeks for roughly 70% of pregnancies. It assumes a regular 28-day cycle with ovulation on day 14, which does not hold for everyone.
An early first-trimester ultrasound, usually between 8 and 14 weeks, is more accurate and is what your doctor will most likely use to confirm or adjust the date.
The date of your last period is usually known exactly, while the date of conception is not. Counting from LMP keeps dating consistent across pregnancies.
Enter your actual average cycle length. A longer cycle shifts the due date later; a shorter cycle shifts it earlier.
Only about 4–5% of babies are born on their exact due date. Most arrive within two weeks either side of it.
Add 280 days (40 weeks) to the first day of your last period, then adjust by the number of days your cycle is longer or shorter than 28.
Yes — add 266 days (38 weeks) to the conception date.