Example 1 — Standard 28-day cycle
- LMP: January 1, 2026
- Cycle length: 28 days
EDD: October 8, 2026
The classic case: 280 days from LMP, no adjustment needed.
Due date calculator (pregnancy, Naegele's rule)
Enter the first day of your last period — we'll estimate your due date (EDD).
We use classic Naegele's rule: first day of last period + 280 days, adjusted if your cycle isn't 28 days. It's obstetrics' usual starting point, not a sure date. Birth often lands ±2 weeks either side — that's normal. Confirm with your doctor, especially with irregular cycles.
Result
Enter the first day of your last period.
How results are calculated
Naegele's rule: EDD = LMP + 280 days (40 weeks), assuming a 28-day cycle with ovulation on day 14.
Cycle adjustment: if your cycle differs from 28 days, we add (or subtract) that difference from the 280 days — a longer cycle shifts the date later, a shorter one earlier.
How to use the calculator
- Enter the first day of your last period (LMP).
- If you know your typical cycle length and it differs from 28 days, enter it — otherwise leave 28.
- Click Calculate or watch the live result as you type.
- Check the pregnancy timeline below the form — it shows LMP, today's position, and the due date.
- Note the EDD and discuss it with your care provider at your next visit.
Usage examples
Example 2 — Shorter cycle (24 days)
- LMP: January 1, 2026
- Cycle length: 24 days
EDD: October 4, 2026
A shorter cycle usually means earlier ovulation, so the due date lands a few days earlier than with a 28-day cycle.
Example 3 — Longer cycle (35 days)
- LMP: January 1, 2026
- Cycle length: 35 days
EDD: October 15, 2026
A longer cycle means later ovulation, so the due date shifts by the same number of days beyond the standard 280.
FAQ
Where do the 280 days come from?
Classic Naegele's rule: add 280 days (40 weeks) from the first day of your last period — the usual obstetric starting point.
What if my cycle isn't 28 days?
Enter your real cycle length and we'll adjust. A longer cycle usually pushes EDD later; a shorter one earlier.
Will the baby definitely arrive that day?
Rarely exactly on the EDD. Most births fall in a window of about ±2 weeks around that date.
What's the difference between period date and conception?
LMP is the first day of bleeding. Conception is usually about two weeks later in a 28-day cycle — so pregnancy weeks are counted from LMP, not conception.
What does EDD stand for?
Estimated Due Date — a planning date for appointments, not a guaranteed delivery day.
Does this replace a dating ultrasound?
No. An early ultrasound often dates the pregnancy more precisely. This calculator is a quick start before your visit.
Why know an approximate due date early?
So you can plan labs, leave, and logistics. An early ballpark makes calendar talks with your doctor easier.
What else is worth opening nearby?
Pregnancy weight gain — range from pre-pregnancy BMI. Ovulation — if you're trying to conceive. BMI — your starting category.