1. The Reality Check

Only about 5% of babies are actually born on their exact calculated due date — but the estimate still matters enormously for prenatal care scheduling, tracking fetal development milestones, and knowing when to expect labor.

2. Plain English Definition

A pregnancy due date calculator estimates the expected delivery date based on the first day of your last menstrual period (LMP), using the standard 40-week (280-day) pregnancy length.

3. Why LMP, Not Conception Date

Most due date calculations count from the last menstrual period rather than the actual conception date, because LMP is far easier to pinpoint reliably, even though conception typically occurs about two weeks later.

4. Key Terms

• LMP: Last Menstrual Period — the first day of your most recent period before pregnancy.
• Gestational Age: How far along the pregnancy is, measured in weeks from the LMP.
• Trimester: Pregnancy is divided into three roughly 13-week trimesters.

5. Next Steps

Calculate your estimated due date above — and remember, it's an estimate, with a normal delivery window spanning about two weeks on either side.