Enter the age of the child and the standard adult dosage into the calculator to determine the child’s dosage.

Young’s Rule Calculator

Enter any 2 values to calculate the missing variable

Young’s Rule Formula

Young’s Rule estimates a child’s medication dose from the child’s age and the standard adult dose. It is an age-based dosing method, so it should be treated as a mathematical estimate rather than a patient-specific prescribing rule.

D_c = \frac{A \cdot D}{A + 12}

Where:

  • Dc = child’s dose
  • A = age of the child in years
  • D = standard adult dose

The formula scales the adult dose by the child’s age. As age increases, the calculated share of the adult dose also increases.

Equivalent Forms

If you know any two values, the relationship can be rearranged to solve for the third.

D = \frac{D_c (A + 12)}{A}
A = \frac{12 D_c}{D - D_c}

The age rearrangement only makes sense when the child’s dose is less than the adult dose.

How to Calculate Young’s Rule

  1. Enter the child’s age in years.
  2. Enter the standard adult dose in the unit you want the answer in, such as mg or mL.
  3. Multiply the child’s age by the adult dose.
  4. Divide that result by the child’s age plus 12.
  5. Interpret the result in the same unit as the adult dose entered.

If the adult dose is entered in milligrams, the answer is in milligrams. If the adult dose is entered in milliliters, the answer is in milliliters.

Example

For a child age 8 and an adult dose of 200 mg:

D_c = \frac{8 \cdot 200}{8 + 12} = 80

The estimated child dose is 80 mg.

Age-to-Dose Reference Table

The table below shows how Young’s Rule changes the child’s estimated dose as age increases.

Child Age Estimated Share of Adult Dose
2 years 14.3%
4 years 25.0%
6 years 33.3%
8 years 40.0%
10 years 45.5%
12 years 50.0%
16 years 57.1%

How to Use the Calculator Correctly

  • Use the dose per administration unless you specifically want to estimate a total daily amount.
  • Keep units consistent. Do not mix mg, mL, tablets, or teaspoons without converting first.
  • If you need a liquid volume, calculate the dose first, then convert using the medication concentration.
  • Round only in a way that matches the actual product strength or measuring device.

When Young’s Rule Is Useful

  • Checking age-based dose calculations for educational purposes
  • Comparing how dose estimates change as a child gets older
  • Reviewing older or legacy dosing methods in a simple format
  • Quickly estimating a proportional child dose from a known adult dose

Important Limitations

  • Young’s Rule uses age only and does not account for weight, body surface area, organ function, drug concentration, or maximum safe dose.
  • Many pediatric medications are better dosed by weight-based or product-specific guidance.
  • The formula is an estimate, not a substitute for professional medical judgment.
  • Always verify any child medication dose against the product label and with a qualified healthcare professional before giving the medicine.

Frequently Asked Questions

Can I enter age in months?

This formula is typically used with age in years. If needed, convert months to a decimal year, but use extra caution because age-only methods are less precise than weight-based dosing.

Can the child’s dose be greater than the adult dose?

For positive ages, Young’s Rule should produce a value lower than the adult dose. If it does not, the inputs or units should be checked.

Does this calculator determine how often a medicine should be given?

No. It estimates the amount per dose only. Dosing frequency must be determined separately.

What if I know the child’s dose and age but need the equivalent adult dose?

Use the rearranged adult-dose form shown above to solve for the standard adult dose from the other two values.