Enter the median toxic dose and median effective dose into the calculator to determine the Therapeutic Index. This calculator can also evaluate any of the variables given the others are known.

Therapeutic Index Formula

The following formula is used to calculate the Therapeutic Index.

TI = TD50 / ED50


  • TI is the Therapeutic Index
  • TD50 is the median toxic dose
  • ED50 is the median effective dose

To calculate the Therapeutic Index, divide the median toxic dose by the median effective dose. The Therapeutic Index is a measure of the safety of a drug, with higher values indicating a safer drug.

What is a Therapeutic Index?

A Therapeutic Index (TI) is a comparison of the amount of a therapeutic agent that causes the therapeutic effect to the amount that causes toxicity. It is used to assess the safety margin of drugs, with a higher TI indicating a safer drug. The closer the TI is to 1, the more likely the drug is to cause toxicity. Therefore, drugs with a high TI are preferred for treatment as they have a wider margin of safety.

How to Calculate Therapeutic Index?

The following steps outline how to calculate the Therapeutic Index (TI) using the formula TI = TD50 / ED50.

  1. First, determine the median toxic dose (TD50).
  2. Next, determine the median effective dose (ED50).
  3. Next, gather the formula from above = TI = TD50 / ED50.
  4. Finally, calculate the Therapeutic Index (TI).
  5. After inserting the values for TD50 and ED50 and calculating the result, check your answer with the calculator above.

Example Problem:

Use the following variables as an example problem to test your knowledge:

TD50 (median toxic dose) = 50

ED50 (median effective dose) = 10