Due Date Calculator

Overview

Calculate your baby's due date using last menstrual period or conception date. See pregnancy week, trimester, and key milestones.

Key Facts

Inputs

How to Use

1. Choose Method — Select LMP (last menstrual period) or conception date method
2. Enter Date — Input the first day of your last period or your conception date
3. View Results — See your due date, current week, trimester, and upcoming milestones

Result Surfaces

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FAQ

How accurate is this due date calculator?

Due date calculators are accurate within 1-2 weeks for most women. Only 5% of babies arrive on their exact due date. First trimester ultrasounds are the most accurate method (±3-5 days). The calculator uses Naegele's Rule: LMP date + 280 days (40 weeks).

Should I use LMP or conception date?

LMP (last menstrual period) is standard because most women know this date. Use conception date if you tracked ovulation or know the exact date. LMP is most accurate for regular 28-day cycles; adjust cycle length in the calculator for irregular cycles.

Why does my doctor's due date differ from this calculator?

Doctors often adjust due dates based on first trimester ultrasound measurements (crown-rump length), which are more accurate than LMP calculations. Ultrasounds before 13 weeks are accurate within ±3-5 days. Accept your doctor's adjusted date if it differs.

Evidence

• src/lib/calculators/registry.ts (metadata)
• src/lib/calculators/page-registry.ts (page/HowTo metadata)
• src/lib/calculators/lifestyle/due-date.ts (calculator config)