health ToolUpdated 2026-09-20
Gestational Age & Pregnancy Due Date Calculator
Track your pregnancy timeline accurately. Enter the first day of your Last Menstrual Period (LMP) to calculate your current gestational age in completed weeks and days, trimester stage, and estimated delivery date.
Formula & Mathematical Methodology
Gestational Age = (Today - LMP) in days; EDD = LMP + 280 Days + (Cycle - 28)
Obstetric clinical practice measures pregnancy from the first day of the last menstrual period, spanning 40 weeks (280 days) for a standard 28-day cycle, using Naegele’s rule.
Step-by-Step Worked Example
Scenario: LMP of April 15, 2026 with 28-day cycle evaluated in September 2026.
1. Count elapsed calendar days from LMP to current date: ~159 days.
2. Divide by 7 to determine weeks: 159 ÷ 7 = 22 weeks and 5 days.
3. Add 280 days to April 15, 2026 to determine Estimated Due Date (EDD): January 20, 2027.
4. Current clinical stage: Second Trimester (Weeks 13–27).
Final Calculated Result: 22 weeks, 5 days (Due: Jan 20, 2027)
Frequently Asked Questions
Why is gestational age counted from the last period instead of conception?
Because the exact date of conception is rarely known with certainty, while the onset of the last menstrual cycle provides a reliable, universally documented physiological benchmark.
Related Calculators
BMI Calculator (Body Mass Index)
Calculate Body Mass Index (BMI) and healthy weight classification.
BMR Calculator (Basal Metabolic Rate)
Calculate your baseline daily calorie burn at complete rest.
Calorie Calculator
Estimate daily calorie requirements based on your physical activity.
Ideal Weight Calculator
Estimate recommended body weight ranges based on height.