Pregnancy Due Date Calculator

What is a pregnancy due date calculator?

A pregnancy due date calculator estimates your expected delivery date (EDD) from the first day of your last menstrual period using Naegele’s rule — LMP plus 280 days — and shows your current week of gestation plus trimester milestones.

How this calculator works

• Enter the first day of your last menstrual period (LMP) and your average cycle length.
• It adds 280 days to the LMP and adjusts for cycles longer or shorter than 28 days.
• It calculates how far along you are today in weeks and days, plus weeks remaining.
• Trimester boundaries are shown: the first ends around 12 weeks, the second around 28.

How to use the result

1. Treat the EDD as a two-week window, not an exact date — only around 5% of babies arrive on their due date.
2. Use your current gestation to schedule screenings and check appointments with your provider.
3. If a later ultrasound dates the pregnancy differently, your provider will usually rely on the ultrasound date — they’re more accurate in the first trimester.
4. Watch trimester milestones only as rough guides for when symptoms and energy levels tend to shift.

How accurate is a due date calculator?

Reasonable for a first estimate, with a real limitation: only about 5% of births land on the calculated date, and a normal, healthy pregnancy can run 37 to 42 weeks. Naegele’s rule assumes a regular 28-day cycle and a known LMP. For irregular cycles or unknown dates, an early ultrasound is the most accurate way to date the pregnancy.

Common mistakes

• Assuming the EDD is exact. A due date is a midpoint estimate, not a deadline.
• Using conception date instead of LMP. Conception typically happens about two weeks after the LMP, so mixing them shifts the date by two weeks.
• Ignoring cycle length. A 35-day cycle means ovulation is later, so the due date shifts accordingly — the calculator handles this.

Due dates anchor the pregnancy timeline, but monitoring your body through it matters more. If you’re also tracking weight and health changes, the BMI calculator can give context, though pregnancy weight targets follow their own IOM ranges — check with your provider.