Calculate a child’s estimated dose in mg from the adult dose and age at next birthday using Cowling’s Rule for ages 1 to 17 years.
Safety note: Educational use only—this is not medical advice. Do not use this tool to dose medication for a child. Pediatric dosing should follow the specific medication label and a clinician/pharmacist’s instructions (often weight-based mg/kg with maximum doses, route, and schedule). This calculator does not account for per-dose vs per-day directions or liquid concentration (mg↔mL). If you suspect an overdose, contact local emergency services or poison control immediately.
Cowling’s Rule Formula
Cowling’s Rule estimates a child’s dose from a known adult dose using the child’s age at the next birthday. It is a historical rule of thumb and should not replace dosing instructions from a clinician, pharmacist, or drug label.
Child\ Dose = \frac{Adult\ Dose \times Age\ at\ Next\ Birthday}{24}- Child Dose is the estimated pediatric dose, usually in milligrams (mg).
- Adult Dose is the standard adult dose of the medication, in the same unit used for the result.
- Age at Next Birthday is the child’s age in whole years at their next birthday.
- 24 is the fixed divisor used in Cowling’s Rule.
The calculator takes the adult dose and multiplies it by the child’s age at their next birthday. It then divides that value by 24 to estimate the child’s dose. For example, a child whose next birthday age is 8 receives an estimated fraction of 8/24, or one third, of the adult dose.
Cowling’s Rule Age Fraction Table
This table shows the adult-dose fraction produced by Cowling’s Rule for common child ages.
| Age at Next Birthday | Formula Fraction | Percent of Adult Dose |
|---|---|---|
| 4 years | 4/24 | 16.67% |
| 6 years | 6/24 | 25.00% |
| 8 years | 8/24 | 33.33% |
| 12 years | 12/24 | 50.00% |
| 16 years | 16/24 | 66.67% |
Example Cowling’s Rule Calculations
Example 1
A medication has an adult dose of 300 mg. The child’s age at next birthday is 8 years.
Child\ Dose = \frac{300 \times 8}{24} = 100The estimated child’s dose is 100 mg.
Example 2
A medication has an adult dose of 500 mg. The child’s age at next birthday is 12 years.
Child\ Dose = \frac{500 \times 12}{24} = 250The estimated child’s dose is 250 mg.
Cowling’s Rule FAQ
What age should you enter for Cowling’s Rule?
Enter the child’s age at their next birthday, not necessarily their current age. For example, if a child is currently 7 years old and will turn 8 on the next birthday, enter 8.
Is Cowling’s Rule safe for all medicines?
No. Cowling’s Rule is only a rough historical estimate. Many medicines require dosing by body weight, body surface area, kidney function, diagnosis, maximum daily dose, or age-specific safety limits. Always check the actual pediatric dosing instructions for the medication.
Can Cowling’s Rule be used for infants?
No. This calculator is not intended for infants. Infant dosing is more sensitive and should be based on medical guidance, weight-based dosing, and the specific medication label or prescription.
