Pregnancy Due Date Calculator

📖 Overview

Calculate your expected due date and current pregnancy week based on your last menstrual period date.

🧪 Example Scenarios

Use these default and higher-pressure example inputs to explore how sensitive this calculator is before using your real numbers.

Input	Base Case	Higher Pressure Case
Year of Last Period	0	0
Month (1-12)	2,025	2,329
Day (1-31)	1	1.15

⚙️ How It Works

Uses Naegele's rule — the standard obstetric method — to estimate the expected date of delivery (EDD) by adding 280 days (40 weeks) to the first day of the last menstrual period (LMP).

The Formula

EDD = LMP + 280 days

LMP	First day of the last menstrual period (entered as year, month, day)
280 days	40 weeks — average length of human pregnancy from LMP
EDD	Estimated Due Date (expected date of delivery)

💡This calculator is scenario-based. Better input quality leads to better decision quality.

⚠️This is an estimate only. Due dates can shift based on ultrasound measurements, cycle length, and other clinical factors. Always confirm with your healthcare provider.

Quick Reference

Weeks pregnant	Trimester	Milestone
1–12	First	Organ formation, heartbeat detectable ~6 weeks
13–26	Second	Movement felt, gender visible on ultrasound
27–40	Third	Rapid growth, lung maturation, birth preparation
37–40	Full term	Baby is considered full term from week 37

When To Use This

Use this tool when you need a fast decision during active planning or execution.
Use this before committing money, time, or tradeoffs that are hard to reverse.
Use this to compare options using the same assumptions across scenarios.

Edge Cases To Watch

Results can be misleading if key inputs are missing, stale, or unrealistic.
Very small or very large values may amplify rounding effects and interpretation risk.
If assumptions change mid-decision, recalculate before acting.

Practical Tips

💡 For irregular cycles, your doctor may adjust the EDD based on early ultrasound dating.

💡 Only about 5% of babies are born exactly on their due date — most arrive within 2 weeks either side.

💡 The calculator also shows current pregnancy week, which is useful for tracking milestones.

Frequently Asked Questions

❓ Why does pregnancy count from the last period, not conception?

Conception date is rarely known precisely, but the LMP is easily remembered and used as a standard reference point.

❓ What is considered full term?

37 to 42 weeks gestation. Before 37 weeks is preterm; after 42 weeks is post-term.

❓ Is my due date a guaranteed delivery date?

No. It is a statistical average. Only about 5% of births happen on the exact due date.