حاسبة العمر الزمني

Chronological age looks like the simplest calculation on this site, and for most purposes it is. The cases where it stops being simple are the ones that matter clinically: correcting age for prematurity, which changes how a baby development is assessed for the first two years, and the different conventions used to describe gestational age, which are a common source of confusion in pregnancy.

المعادلة

Age = current date - date of birth, expressed in years, months and days
Corrected age = chronological age - (40 weeks - gestational age at birth)

• Corrected age applies to infants born before 37 weeks
• Gestational age at birth is counted in completed weeks from the first day of the last menstrual period

Corrected age convention follows standard paediatric practice for assessing preterm infants.

Corrected age for preterm infants

A baby born at 28 weeks is 12 weeks short of term. When that baby is six months old by the calendar, their corrected age is three months, and developmental milestones are assessed against three months, not six. Using chronological age instead makes a normally developing preterm infant appear delayed, which causes avoidable alarm and occasionally unnecessary referral.

The convention is to correct until about two years of age, by which point the difference has become proportionally small and most preterm infants have caught up. Correction is used for developmental assessment and growth charting; it is not used for the immunisation schedule, which follows chronological age because immune response depends on time since birth rather than on maturity.

Gestational age conventions

Gestational age is counted from the first day of the last menstrual period, not from conception, which makes a pregnancy nominally 40 weeks long even though fertilisation occurs about two weeks in. Fetal or conceptional age is therefore roughly two weeks less than gestational age, and mixing the two is a frequent source of confusion when comparing sources.

Term itself is subdivided rather than being a single threshold: early term is 37 weeks 0 days to 38 weeks 6 days, full term 39 weeks 0 days to 40 weeks 6 days, late term 41 weeks, and post-term from 42 weeks. The distinction exists because outcomes differ measurably across those bands.

• Preterm is before 37 weeks 0 days, subdivided into extremely preterm under 28 weeks, very preterm 28 to 32, and moderate to late preterm 32 to 37.
• An ultrasound-derived due date in the first trimester is more accurate than one from the last menstrual period and normally supersedes it.

Age conventions elsewhere

Not every system counts age the way the calendar does. East Asian age reckoning, still encountered socially in parts of the region, counts a newborn as one year old and adds a year at the lunar new year rather than on a birthday, which can put a person up to two years above their chronological age. South Korea moved to international age for legal and administrative purposes in 2023.

For anything medical or legal, chronological age from date of birth is the operative figure. The other conventions matter mainly when reconciling documents or interpreting a self-reported age.

حدود الاستخدام

• Corrected age is a convention for interpreting development, not a statement about a child. Concerns about development should be assessed by a clinician regardless of what a correction suggests.
• Correction beyond about two years is not standard practice and can mask a genuine delay.
• Gestational age itself is an estimate unless conception was documented, and estimates from last menstrual period carry more uncertainty than early ultrasound dating.
• Date arithmetic across time zones, leap years and the end of a month can differ by a day depending on the convention used, which matters for precise clinical calculations.
• This tool does not assess development, growth or maturity, only elapsed time.
• For medication dosing in children, weight and body surface area usually matter more than age, and age alone should not be used.

الأسئلة الشائعة

What is corrected age for a premature baby?

Chronological age minus the number of weeks the baby was born early. A baby born at 28 weeks who is six months old by the calendar has a corrected age of three months, and developmental milestones are assessed against three months.

How long should I use corrected age?

Until about two years, for developmental assessment and growth charting. By then the difference is proportionally small and most preterm infants have caught up.

Do vaccines follow corrected or chronological age?

Chronological age. The immunisation schedule is based on time since birth rather than maturity, so preterm infants are vaccinated on the same calendar schedule as term infants.

Why is pregnancy 40 weeks if conception is only 38 weeks before birth?

Because gestational age is counted from the first day of the last menstrual period, about two weeks before ovulation and conception. Fetal or conceptional age is roughly two weeks less than gestational age.

What counts as full term?

Full term is 39 weeks 0 days to 40 weeks 6 days. Early term is 37 to 38 weeks 6 days, late term is 41 weeks, and post-term is 42 weeks and beyond. The bands exist because outcomes differ measurably between them.

المراجع

1. MedlinePlus. Premature babies.
2. MedlinePlus. Gestational age.
3. American College of Obstetricians and Gynecologists. How Your Fetus Grows During Pregnancy.
4. MedlinePlus. Infant and newborn development.