Enter the total daily dose and the weight of the patient into the calculator to determine the dose rate in milligrams per kilogram per day (mg/kg/day). You can also solve for any missing variable (total daily dose, weight, or mg/kg/day). If you only know an amount per dose (mg, g, or mL), use the second tab to convert it to mg/kg/day using doses per day.
Medical disclaimer: This calculator is for educational purposes only and does not provide medical advice or dosing recommendations. Always follow the prescription/label and confirm calculations and units (mg vs mL; mg/mL concentration) with a licensed clinician or pharmacist—especially for children, pregnancy, and kidney/liver disease. Do not use this tool to start, change, or stop any medication.
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Mg/Kg/Day Formula
The following formulas are used to calculate the dose rate in milligrams per kilogram per day (mg/kg/day).
R = \frac{T}{W}
\quad\text{and}\quad
R = \frac{P \times N}{W}Variables:
- R is the dose rate in milligrams per kilogram per day (mg/kg/day)
- T is the total daily dose in milligrams per day (mg/day)
- W is the weight of the patient in kilograms (kg)
- P is the amount per dose in milligrams per dose (mg/dose)
- N is the number of doses per day (times/day)
If you already know the total daily dose (T), calculate mg/kg/day by dividing by weight: R = T ÷ W. Doses per day (N) only matters when you start from an amount per dose (P), where T = P × N.
What is a Mg/Kg/Day?
Mg/Kg/Day is a unit of measurement often used in pharmacology and toxicology to indicate the dose rate or exposure level of a substance. It stands for milligrams per kilogram per day. This means the amount of a substance (in milligrams) given or received per kilogram of body weight per day. It is used to standardize values based on body weight, allowing for more accurate comparisons and calculations.
How to Calculate Mg/Kg/Day?
The following steps outline how to calculate mg/kg/day using R = T / W (or, if starting from per-dose dosing, T = P × N first).
- Determine whether you have a total daily dose (T, mg/day) or an amount per dose (P) and doses per day (N).
- Convert units if needed: grams to milligrams (g → mg) and pounds to kilograms (lb → kg).
- If you have per-dose dosing, calculate the total daily dose: T = P × N (if dosing in mL, convert to mg using the concentration in mg/mL first).
- Calculate the dose rate: R = T ÷ W.
- Double-check that you entered the correct units (mg vs mL; mg/mL concentration) and compare the result with the calculator above.
Example Problem :
Use the following variables as an example problem to test your knowledge.
Total daily dose (T) = 500 mg/day
Weight of the patient (W) = 70 kg
Number of doses per day (N) = 3
mg/kg/day (R) = 500 ÷ 70 = 7.14 mg/kg/day. (If taken 3 times/day, the total daily dose is still 500 mg/day; it would be about 166.67 mg per dose.)
