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Adjusted Age Calculator: Corrected Age for Prematurity

What is this tool?

The adjusted age calculator, also called the corrected age calculator, finds a premature baby's corrected age: the age counted from the due date instead of the actual birth date, shown next to the baby's chronological age. A baby born 8 weeks early has had 8 fewer weeks of development than a baby born on the due date, so for developmental milestones in the first two years, clinicians often use the corrected age rather than the age from birth. Enter the birth date and how many weeks early the baby was, and the calculator gives both ages side by side. This page is informational only and is not medical advice; confirm any figure that matters with your paediatrician.

How it works

Corrected age is calculated in two steps. First, find the due date: the birth date plus the number of weeks premature, times seven days. A baby born 8 weeks early has a due date 56 days after the birth date. Second, calculate the age from that due date to today, using the same completed years, months and days arithmetic as the main age calculator. The chronological age, counted from the actual birth date, is shown next to it so the size of the correction is always visible. A baby born at full term, 40 weeks, has no correction, and the two ages are the same.

Worked example

Worked example: born 1 August 2026 at 32 weeks of pregnancy, which is 8 weeks early. The due date is 1 August plus 56 days, which is 26 September 2026. On 23 October 2026 the chronological age is 2 months and 22 days, and the corrected age is 27 days, because only 27 days have passed since the due date. For milestone purposes, this baby is counted as about one month old, not nearly three months old.

When to use it

Corrected age matters most in the first two years, when development is measured in weeks and months and a few weeks make a real difference. A baby born two months early who is six months old by birth date is only four months old by corrected age, and judging that baby against six-month milestones would be judging against the wrong standard. That is why health visitors, paediatricians and early-years services ask for corrected age: it compares the child with babies at the same stage of development, not just the same calendar age.

Parents use it for the same reason, and for a more personal one: it answers the question of whether a baby is on track without the worry that comes from comparing with babies born on time. A corrected age that is lower than the chronological age is not a delay; it is the adjustment that makes the comparison fair. The gap between the two ages closes as the child grows, because a fixed number of weeks becomes a smaller share of the child's age, and by around two years most services stop using the correction.

• Parents checking developmental milestones for a baby born early.
• Health visitors and paediatricians recording age for a premature baby.
• Early-years and nursery staff placing a child in the right age group.
• Comparing a premature baby's progress with babies born on time, fairly.
• Working out when to expect milestones, such as sitting, crawling or first words, on the corrected timescale.

Corrected age is a clinical convention, not a legal age. For legal purposes, such as school admission or benefits, the chronological age from the actual birth date is what counts, unless a specific rule says otherwise. If a form asks for age without specifying, give the chronological age and mention the corrected age separately where it is relevant.

Step by step

Using this page takes three inputs and gives two ages, so the correction is never hidden.

1. Enter the baby's actual date of birth in the first field.
2. Enter how many weeks of pregnancy had passed at birth, for example 32. The calculator works out how many weeks early that is against a full term of 40 weeks, and from that the due date.
3. Enter the reference date, which defaults to 23 October 2026 in the worked example. Change it to today, or to any date you want the ages on.
4. Read both results: chronological age from the birth date, and corrected age from the due date. The due date itself is shown so the calculation can be checked.

The due date shown is the one implied by the weeks-early figure, not necessarily the due date from the pregnancy record. If the recorded due date differs, for example because an ultrasound revised it, use the recorded due date instead: enter the weeks-early figure that produces it, or work from the due date directly by checking the gestational age page. The corrected age depends on the due date, so a due date that is a week out moves the corrected age by a week.

One more note: the reference date matters more here than on most pages, because corrected ages change fast in the early months. A result read today is not the result for next week, and a milestone checked against last month's corrected age will be a month out. Always note the date alongside the corrected age.

Common mistakes

The most common mistake is subtracting the weeks early from the chronological age in the wrong units. Eight weeks early does not mean eight weeks off the months figure in a simple subtraction, because months are calendar months and weeks are seven days. The correct method is the one this page uses: add the weeks to the birth date to get the due date, then count calendar months and days from the due date. Subtracting 56 days from the chronological age in days gives the same answer, but subtracting 8 from a month count does not.

The second mistake is using corrected age for too long, or for the wrong purpose. Corrected age is for developmental milestones in roughly the first two years. After that, the correction is small compared with the child's age and most services stop using it. Using it at school age, or on a legal form, creates confusion rather than fairness, because the systems that read those forms expect chronological age.

• Subtracting weeks early from a month count instead of working from the due date.
• Counting four weeks as one month when working out the correction.
• Using corrected age after about two years, when services have stopped using it.
• Using corrected age on legal or school forms that expect chronological age.
• Using an estimated due date when the recorded due date is different.
• Forgetting that the corrected age can be negative before the due date, which simply means the baby has not yet reached the due date.

A further mistake is treating the corrected age as a judgement on the baby. It is not. A lower corrected age does not mean a baby is behind; it means the comparison standard has been adjusted so the baby is judged fairly. The corrected age is a tool for fair comparison, not a score, and a baby whose corrected age is used properly is being measured against the right yardstick.

More worked examples and notes

The examples below use the same method as the worked example, and each can be checked by entering the same figures into the tool.

• Born 1 June 2026 at 28 weeks, which is 12 weeks early. The due date is 1 June plus 84 days, which is 24 August 2026. On 23 October 2026 the chronological age is 4 months and 22 days, and the corrected age is 1 month and 29 days.
• Born 1 August 2026 at 32 weeks, which is 8 weeks early. The due date is 26 September 2026. On 23 October 2026 the chronological age is 2 months and 22 days, and the corrected age is 27 days. This is the worked example from the main part of the page.
• Born 1 August 2026 at 40 weeks, full term. There is no correction, so the chronological age and the corrected age are both 2 months and 22 days on 23 October 2026. The calculator shows this directly: with 40 weeks entered, the due date equals the birth date.
• Born 1 August 2026 at 36 weeks, which is 4 weeks early. The due date is 29 August 2026. On 23 October 2026 the chronological age is 2 months and 22 days, and the corrected age is 1 month and 24 days.
• Before the due date: born 1 October 2026 at 32 weeks, due 26 November 2026. On 23 October 2026 the chronological age is 22 days, and the corrected age has not started yet, because the due date is still in the future. The calculator says so rather than showing a negative age.

The pattern across these examples is the point: the correction is largest, in proportion, in the earliest months, and it shrinks as the child grows. A 12-week correction on a 4-month-old is a third of the child's life; the same 12 weeks on a 2-year-old is a small fraction. That is why services use the correction early and drop it later, and why the two ages are shown together here rather than the corrected age alone.

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Frequently asked questions

Written and checked against the calculator above. Last updated: 23 October 2026. Calculation runs entirely in your browser — no date is sent to a server. This tool gives calendar results only, not medical, legal or financial advice. This tool gives informational results only, not medical advice. Confirm any figure that matters for care or milestones with your paediatrician.