Pediatric Dosing Calculator
Calculate age- and weight-adjusted medication doses for children using Young's, Clark's, and Fried's rules.
About this calculator
This calculator applies three classic pediatric dose-scaling rules to a given adult dose: Young's Rule (age / (age + 12) x adult dose, using age in years), Clark's Rule (weight in kg / 70 x adult dose), and Fried's Rule for infants under 2 (age in months / 150 x adult dose). Of the three primary inputs, Adult Dose moves Young's Rule Dose the most -- since Young's Rule multiplies the adult dose directly by an age-based fraction, a given percentage change in Adult Dose produces exactly that same percentage change in the output, while an equivalent percentage change in the child's age moves the age/(age+12) fraction by a smaller amount because that fraction grows more slowly than age itself. Child's Weight has no effect at all on Young's Rule Dose -- Young's Rule is age-only by definition, so weight only enters through Clark's Rule and the BSA-based estimate, not through Young's or Fried's.
All three rules are approximations that predate modern weight-based (mg/kg) dosing, which current pediatric guidelines from the FDA and AAP consider the standard for most medications; these classic rules exist mainly as a reference or cross-check, not a replacement for a drug-specific mg/kg dose from current labeling or a source like the Harriet Lane Handbook or BNF for Children. Two further notes on what this calculator displays: Fried's Rule Dose only applies to infants under 2 years old by definition, so outside that range this calculator shows "N/A (age >= 2)" rather than a computed number -- a bare 0 mg would misleadingly read as a real (if tiny) dose rather than "this rule doesn't apply here." Clark's Rule Dose is capped at the adult dose: uncapped, a large child (over 70 kg) would compute to MORE than the adult dose, which defeats the purpose of a dose-scaling-down estimate. Finally, the Average (Young/Clark) output is this calculator's own composite -- a simple mean of the Young's and Clark's Rule figures -- not a named, separately published clinical dosing formula; treat it as a convenience cross-check between the two rules above it, not as a fourth independently-validated method.
Medical Disclaimer
This calculator is for informational and educational purposes only. It is not a substitute for professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare provider before making decisions about your health. Never disregard professional medical advice or delay seeking it because of results from this tool.
This tool estimates a starting point only and is not a validated clinical decision-support system. It does not account for every patient-specific factor (organ function, drug interactions, allergies, comorbidities, or current clinical status). Any dose, rate, or setting must be independently verified by the treating clinician and pharmacist or respiratory therapist against current institutional protocols, product labeling, and the patient's full clinical picture before being administered or applied.
Inputs
AAP: weight-based dosing standard; typical pediatric weights: 6 mo 7 kg; 1 yr 10 kg; 5 yr 18 kg; 10 yr 32 kg
Results
Young's Rule Dose
166.7mg
Clark's Rule Dose
142.9mg
How to Use This Calculator
- Enter the child's age (years — use decimals for months, e.g. 0.5 = 6 months) and weight (kg).
- Enter the standard adult dose of the medication in milligrams.
- Review the calculated pediatric doses from Young's Rule, Clark's Rule, Fried's Rule (infants under 2), and a BSA-based estimate, plus the Young's/Clark's average.
- Always verify with current Harriet Lane or BNFc guidelines — this tool is for reference only.
How the result changes with Adult Dose
| Adult Dose | Young's Rule Dose | Clark's Rule Dose |
|---|---|---|
| 250 | 83.3mg | 71.4mg |
| 375 | 125mg | 107.1mg |
| 750 | 250mg | 214.3mg |
| 1,250 | 416.7mg | 357.1mg |
What each input means
- Child's Age
- Age of the child in years. Use decimals for months (e.g., 0.5 = 6 months).
- Child's Weight
- Child's body weight in kilograms. Weight-based dosing (mg/kg) is standard for pediatrics per FDA pediatric labeling and AAP guidelines. Always verify calculated dose against maximum adult dose and product labeling.
- Adult Dose
- Standard adult dose of the medication in milligrams.
What each result means
- Clark's Rule Dose
- Capped at the adult dose — weight/70 × adult dose would otherwise exceed the adult dose entirely for children over 70 kg.
- Fried's Rule Dose (infants)
- Only valid for infants under 2 years old. Shows "N/A (age >= 2)" outside that range rather than a misleading 0 mg.
- Average (Young/Clark)
- This calculator's own composite (mean of Young's and Clark's Rule) — not a named, separately published clinical formula.
How this is calculated
Worked example, using the default values
- Identify Input ParametersChild's Age = 6, Child's Weight = 20, Adult Dose = 500 = 3 input(s) provided
- Calculate Young's Rule DoseYoung's Rule Dose166.7 = 166.7
- Calculate Clark's Rule DoseClark's Rule Dose142.9 = 142.9
- Calculate Fried's Rule DoseFried's Rule DoseN/A (age >= 2) = N/A (age >= 2)
- Calculate BSA-Based DoseBSA-Based Dose213 = 213
Engine last updated . Built by Paul Gunder, a software engineer, not a licensed financial, medical, or legal professional.
Frequently Asked Questions
Which input changes the Young's Rule dose the most — age, weight, or the adult dose?
Adult Dose has the largest effect on Young's Rule Dose. Young's Rule multiplies the adult dose directly by the fraction age/(age+12), so a given percentage change in the adult dose produces that exact same percentage change in the output. The same percentage change in the child's age moves the age/(age+12) fraction by a smaller amount, because that fraction rises more slowly than age itself does.
Does a child's weight affect the Young's Rule dose?
No. Young's Rule is defined purely from age -- the formula is age/(age+12) x adult dose, with no weight term at all. Weight only enters this calculator through Clark's Rule (weight/70 x adult dose) and the BSA-based estimate. If two children are the same age but different weights, this calculator's Young's Rule Dose is identical for both.
What's the difference between Young's Rule, Clark's Rule, and Fried's Rule?
Young's Rule scales the adult dose by age alone (age/(age+12)), Clark's Rule scales it by weight alone (weight in kg / 70), and Fried's Rule is a version of Young's Rule intended specifically for infants under 2 years old, scaling by age in months (months/150). This calculator reports all three plus a body-surface-area-based estimate, because they can diverge noticeably for a child whose weight is unusually high or low for their age.
Should these classic dosing rules be used instead of a weight-based (mg/kg) dose?
No. Young's, Clark's, and Fried's rules predate modern weight-based dosing and are considered historical approximations rather than the current standard. FDA pediatric labeling and AAP guidelines favor mg/kg dosing derived from a drug's actual pediatric studies. These rules are useful as a rough cross-check or reference, not a substitute for a drug-specific dose from current labeling, the Harriet Lane Handbook, or the BNF for Children.
Is the Average (Young/Clark) output a recognized clinical dosing formula?
No -- it's this calculator's own composite, not a named or separately published clinical formula. It's simply the arithmetic mean of the Young's Rule Dose and Clark's Rule Dose figures above it, offered as a convenience cross-check for when those two rules disagree, not as a fourth independently-validated dosing method. Treat it the same way as the individual rules: a rough reference, not a substitute for a drug-specific mg/kg dose from current labeling.
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