Enter the adult dose and the child’s age (in months) into the calculator to estimate the child’s dose using Fried’s Rule.
Medical disclaimer: This calculator demonstrates Fried’s Rule for educational/historical purposes only and is not medical advice. Do not use it to dose medications for children—pediatric dosing should follow the specific drug’s official labeling and clinician/pharmacist guidance (typically weight-based mg/kg, with maximums and other adjustments). This tool does not account for formulation/concentration (mg/mL) or safe rounding to measurable doses.
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Fried's Rule Formula
The following formula is used to estimate an infant’s drug dose from an adult dose using Fried's Rule.
Dc = (Da * a) / 150
Variables:
- Dc is the child's dose (in the same dose unit as Da, such as mg)
- Da is the adult dose (in the same dose unit as Dc, such as mg)
- a is the child's age (months)
To calculate the child's dose, multiply the adult dose by the child's age in months. Then, divide the result by 150. This gives an estimate according to Fried's Rule.
What is Fried's Rule?
Fried's Rule is an older age-based method used to estimate an infant's drug dose from an adult dose using the infant's age in months. It is generally intended for infants (often under about 2 years of age) and follows the relationship: child dose = (age in months / 150) × adult dose. In modern clinical practice, pediatric dosing is typically based on the specific medication’s labeling and factors such as weight (mg/kg), maximum doses, indication, and organ function.
Limitations and safer approach
Age-based “rules” like Fried’s do not account for medication formulation, concentration, dosing frequency, contraindications, or drug-specific pediatric guidance. For real-world dosing, check the drug’s official prescribing information (e.g., FDA labeling) and follow a pediatrician or pharmacist’s instructions.
