Generally, as preterm infants are born several weeks early, this may lead to discrepancies in their specific months of age. If the preterm baby is developing well without other complications, it is possible to calculate the corrected age. Under normal circumstances, the simplest method to calculate the corrected age is to use the expected due date for calculation. Corrected age is calculated by taking the current age in days and subtracting the expected due date, which allows for accurately estimating the baby's current age in months. When the baby is between two and two and a half years old, you can add back the months previously subtracted, and calculate according to the normal age since, by then, the baby's developmental indicators are generally the same as those of a full-term baby.