Contrast Card Generator

Corrected age: reading a premature baby's vision by their due date

If your baby arrived early, their vision runs on the timetable that started at the due date, not the birth date — and using that "corrected age" is the difference between a card they can see and a card that is fog.

Established scienceUpdated Sep 1, 2026For parents, caregivers

Well-supported by peer-reviewed research.

In one line

If your baby arrived early, their vision runs on the timetable that started at the due date, not the birth date — and using that “corrected age” is the difference between a card they can see and a card that is fog.

Key points

  • Corrected age = how old your baby would be if they had arrived at term. Take the calendar age and subtract how early they came: a baby born at 34 weeks is six weeks early, so at four months old their corrected age is about two and a half months.
  • Vision develops on the corrected clock. The visual system matures on its own biological schedule, which began at conception, not at delivery. A healthy baby born six weeks early at two months old sees roughly like a two-week-old — because developmentally, that is what their visual system is.
  • For pattern cards this is the one adjustment that matters most. Every “what can they see at N months” table — sharpness, contrast, colour, tracking — is indexed by corrected age. Using the calendar age instead picks patterns too fine and too busy for what the baby can currently resolve: the one sizing error that makes a card unreadable rather than merely easy (What your baby can actually see, month by month).
  • It is a subtraction, never an addition. Babies born at or after term get no adjustment in the other direction — corrected age exists only so an early arrival isn’t held to a timetable they never started.
  • It fades out. Clinical practice applies correction through roughly the first two years; after that the few weeks of difference stop being meaningful for most children. (For vision-card purposes it matters most in the first six months, when ability changes fastest.)
  • Healthy preterm babies mostly track their corrected-age norms. The research is nuanced — a few studies even find slightly sharper vision at term-equivalent age than term newborns, plausibly from the extra weeks of looking; studies also find delays where there are complications. Corrected age is the sound default; your baby’s own team knows if their case differs.

How this tool applies it

Tell the generator the baby’s age and, if they arrived early, the gestational age at birth in weeks — the “born at 34 weeks” number from the discharge summary. It does the subtraction itself and sizes every feature from the corrected age (the readout shows you: born 6 weeks early · corrected age 1 month). No birth date is ever asked for or stored. The story of designing that control — and why it asks for the number families are actually told — is its own article: Corrected age, on a slider.

The evidence

  • [established science / practitioner guidance] Correcting for prematurity when assessing early development, through roughly two years, is standard clinical practice.
  • [established science] Preterm infants’ visual development is assessed against corrected age in the clinical literature, and healthy preterm infants track close to corrected-age norms; complications (not prematurity itself) are the main source of delays. See the sourced summary in docs/02-research/03-prematurity-and-corrected-age.md.
  • [established science] Babies born prematurely need clinician-led eye care on its own schedule — see the screening statements in the sources and ROP and prematurity: what parents should know. Nothing about corrected age replaces that.
  • [our design opinion] Asking for gestational age at birth (rather than “weeks premature”, which nobody is told) and doing the arithmetic in the tool is our design choice, made to remove a quiet error path from the most stressed audience this site has.

Practical takeaways

  • Count vision expectations — and card choices — from the due date, not the birth date, for roughly the first two years.
  • Enter the “born at N weeks” number in the generator and let it translate; watch the corrected-age readout to see what stage is actually being designed for.
  • Don’t panic-compare with term babies of the same calendar age. Six weeks is a huge fraction of a three-month-old’s life; the corrected clock is the fair one.
  • Keep every eye appointment. Corrected age sizes a card; it does not monitor eyes — that is your ophthalmology team’s job, especially after an early arrival.

Caveats & disclaimer

Educational, not medical, and not a developmental assessment. Corrected age here is used only to choose a pattern size. Individual variation is large; premature babies — especially very early arrivals — should be followed by their own paediatric and ophthalmology team, whose guidance overrides anything a printed card implies. If clinicians have noted your baby tracking ahead of or behind corrected-age norms, follow their reading, not the default.