IC50 Calculator
How to calculate an IC50
- Enter each concentration with its responses, such as % activity or % viability, one concentration per line. Replicates can go on the same line.
- Tick Fix bottom at 0 and top at 100 if your responses are normalized to controls and the data do not reach both plateaus.
- The IC50 (or EC50 for a rising curve) appears with the Hill slope, top, bottom and R², and the fitted curve is drawn.
Frequently asked questions
Which model is fitted?
The four-parameter logistic: response = bottom + (top − bottom) ÷ (1 + 10^((log IC50 − log concentration) × Hill slope)), fitted to every replicate by least squares. It is the standard sigmoidal dose-response model.
IC50 or EC50?
IC50 is the concentration that gives half the maximal inhibition, for a falling curve; EC50 is the concentration that gives half the maximal effect, for a rising curve. The tool names the result by the direction of your data.
What does the Hill slope mean?
How steep the curve is. A slope of −1 (falling) or 1 (rising) is a standard curve; steeper values suggest cooperative binding, shallower ones heterogeneous responses.
How many concentrations do I need?
At least 4, and 6 to 10 spread across both plateaus give a reliable fit. Concentrations must be above zero, because the fit uses their logarithm.