Health
Pregnancy Due Date Calculator
By the Dailycaltor team · formula-verified · last updated July 2026
Estimated due date from your last period.
Details
Formula
Naegele's rule: due date = first day of last menstrual period + 280 days (40 weeks), adjusted by (cycle length − 28) for longer or shorter cycles. Only about 1 in 20 babies arrives exactly on the due date — most come within two weeks either side.
Worked examples
- LMP 1 Jan with a 28-day cycle → due ~8 Oct.
- A 32-day cycle shifts the estimate 4 days later.
- At 14 weeks you are in the second trimester.
Common mistakes
- Counting from conception instead of the last period — pregnancy weeks start at LMP.
- Treating the due date as exact; it is the middle of a window.
- Not updating the estimate after a dating ultrasound, which is more accurate.
Source: Naegele's rule (280 days from LMP). Last updated: July 2026. Educational estimates only.
Questions
How is a due date calculated?
Add 280 days (40 weeks) to the first day of your last period, adjusted for your cycle length.
How accurate is the due date?
It is an estimate — only ~5% of births land on the exact date; ultrasounds refine it.
How many weeks pregnant am I?
Count from your LMP, not conception. The tool shows weeks and days today.
When do trimesters change?
Commonly: weeks 1–12 first, 13–26 second, 27–40 third (definitions vary slightly).
What if my cycles are irregular?
LMP dating is less reliable then — an early ultrasound gives the best estimate.
Is this medical advice?
No — it is educational. Confirm dating and care with your doctor or midwife.