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Child Dose By Age Calculator

Work out child dose by age instantly with clear inputs, formula shown and shareable results.

About Child Dose By Age Calculator

Applies the historical age-based dosing rules, Fried's for infants and Dilling's for older children, both of which scale the adult dose by age.

Formula

Age-based rules

Fried's rule: child dose = adult dose x age in months / 150. Dilling's rule: child dose = adult dose x age in years / 20

Worked example

With the default values below, Child Dose By Age Calculator returns Estimated child dose of 60.0. Change any input above and every figure here is recalculated in your browser.

Inputs used

Adult doseaccepts 1–5,000 mg
500 mg
Child ageaccepts 1–240 months
18 months
Ruleone of Fried's rule (infants, age in months / 150), Dilling's rule (age in years / 20)
Fried's rule (infants, age in months / 150)

Results

Estimated child dose
60.0 mg
Fraction of the adult dose
0.120
Share of the adult dose
12.0%
Rule applied
Fried's rule

Step by step

  1. 1Values used
  2. 2Age-based rules
  3. 3Estimated child dose= 60.0 mg
  4. 4Fraction of the adult dose= 0.120
  5. 5Share of the adult dose= 12.0
  6. 6Rule applied= Fried's rule

Assumptions and limits

  • The result is derived only from the 3 inputs listed above. Anything not among them is not part of the calculation.
  • In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
  • Figures are rounded for display to 3 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
  • Educational estimate only. Not a substitute for professional clinical judgement, and must not be used to make treatment or dosing decisions.
  • This is an estimate for general information and not professional medical advice. See the full disclaimer for the limits that apply to this kind of calculator.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Educational estimate only. Not a substitute for professional clinical judgement, and must not be used to make treatment or dosing decisions.

Frequently Asked Questions

Are these rules used clinically?

No. Modern practice uses mg/kg or mg/m2 values from a paediatric formulary; these rules are historical teaching aids.

Why are they unreliable?

Drug clearance depends on organ maturity and body size, neither of which tracks age closely enough.

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