Pregnancy Countdown Calculator
Calculate your due date, current pregnancy week, and countdown to birth.
Track your pregnancy week by week — enter your due date or last menstrual period to get started.
How pregnancy is measured
Gestational age vs foetal age
Pregnancy is measured from the first day of your last menstrual period (LMP), not conception. This means you are technically "2 weeks pregnant" at the moment of conception, making a full-term pregnancy 40 weeks from LMP. To find the exact date that is 40 weeks from your last period, use the date calculator.
The three trimesters
The first trimester runs from weeks 1–12, the second from weeks 13–26, and the third from weeks 27–40. Each marks distinct stages of foetal development and different experiences for the mother. For counting the days and weeks to your due date, the day counter calculates the exact number of days between any two dates.
Due date accuracy
Only about 5% of babies are born on their exact due date. A normal full-term pregnancy runs from 37 to 42 weeks. Dates given here are estimates — always follow advice from your midwife or doctor. For tracking your baby's age in weeks after birth, try the age calculator.
About this calculator
This tool uses a standard 280-day (40-week) pregnancy based on a 28-day cycle. Results are estimates only and should not replace professional medical guidance.
Worked example
LMP: 1 October 2025. Estimated due date: 8 July 2026 (280 days / 40 weeks). End of first trimester (week 12): 24 December 2025. Anatomy scan window (week 18–21): 18 February 2026. Third trimester begins (week 28): 25 March 2026. Only ~5% of babies arrive on the exact due date — always confirm milestones with your midwife or doctor.
Frequently Asked Questions
How is pregnancy measured in weeks?
Pregnancy is measured from the first day of your last menstrual period (LMP), not the date of conception. This means you are technically '2 weeks pregnant' at conception, making a full-term pregnancy 40 weeks (280 days) from LMP. Your midwife or doctor may adjust dates after an early ultrasound.
What are the three trimesters of pregnancy?
The first trimester runs from weeks 1–12, the second from weeks 13–26, and the third from weeks 27–40. Each trimester marks distinct stages of foetal development and different physical experiences for the mother. Most prenatal screening tests are timed in relation to these trimester boundaries.
How accurate is a due date calculator?
Due dates calculated from LMP are estimates only — just 5% of babies are born on their exact due date. A normal full-term pregnancy runs from 37 to 42 weeks. An early ultrasound scan (before 14 weeks) provides a more accurate due date based on foetal measurements.
What is the difference between gestational age and foetal age?
Gestational age is measured from the first day of the last menstrual period — the standard used by doctors. Foetal age (embryonic age) is measured from conception — approximately 2 weeks less than gestational age. When your care team says '12 weeks pregnant,' they mean gestational age.
Evidence & Methodology
How This Page Is Grounded
Method
Estimates a due date as 280 days from the first day of the last menstrual period and derives milestones from gestational age.
Important limitation: Due dates are estimates and cycle length, conception timing and clinical dating scans can change them.
Primary Sources
Quality Checks
280-day arithmetic, trimester milestones and leap-year crossings are checked.
See how sources are selected and corrections are handled in our Editorial & Calculation Methodology, and which automated checks this page has to pass in How We Test.