Pregnancy Due Date Calculator
Estimate your pregnancy due date from the first day of your last menstrual period using Naegele's rule, the standard method used by most due-date calculators and many healthcare providers.
Estimated due date
October 8, 2026
Estimated conception
January 15, 2026
First trimester ends
April 2, 2026
Second trimester ends
July 9, 2026
How it's calculated
Naegele's rule estimates your due date as 280 days (40 weeks) after the first day of your last menstrual period (LMP) — this assumes a typical 28-day cycle with ovulation around day 14.
Conception is estimated at roughly 14 days after your LMP, which is also when your pregnancy "age" starts to differ from your cycle-based due date calculation — pregnancies are dated from LMP by convention, even though conception happens about two weeks later.
This is an estimate, not a guarantee — only a small percentage of babies are born exactly on their estimated due date. Ultrasound measurements later in pregnancy can refine this estimate further.
Worked example
If your last menstrual period started on March 1, your estimated due date (LMP + 280 days) would be December 6 of that year, with an estimated conception date around March 15.
Your estimated first trimester would end around May 31 (13 weeks from LMP), and your second trimester would end around September 6 (27 weeks from LMP).
Frequently Asked Questions
- Why is my due date based on my last period instead of conception?
- Pregnancies are dated from the first day of your last menstrual period by medical convention, since that date is usually known precisely, while the exact date of conception often isn't. This means your pregnancy is considered about 2 weeks further along than conception itself.
- How accurate is a due date calculated this way?
- Naegele's rule assumes a standard 28-day cycle with ovulation on day 14 — if your cycle is longer or shorter, your actual due date may differ. An early ultrasound often provides a more precise estimate.
- What if I don't know the exact date of my last period?
- If you're unsure, use your best estimate — or consult a healthcare provider, who may use an ultrasound to estimate gestational age more precisely, especially if your cycle is irregular.