Estimated potency, trust assessment, and recommended next concentration range will appear here.
Assay Analysis & Quality Control
IC50 / EC50 Calculator
Fit normalized dose-response data with a standard 4-parameter logistic model to estimate IC50 for inhibition assays or EC50 for activation assays. Visualize the fitted curve, review fit quality, assess whether the estimate is trustworthy, and identify the next concentration range to test.
IC50 / EC50 Calculator
Use increasing for percent inhibition, percent activation, or reporter signal normalized upward. Use decreasing for percent viability or activity remaining.
Expected format: Concentration Response 1 Response 2 Response 3
Results
Fit Summary
4PL fit metrics will appear here.
Data Table
Parsed concentration-response rows will appear here.
Dose-Response Curve
Graph will appear after calculation.
Lab Summary Card
Export-ready summary will appear here.
Formula and Calculation Logic
IC50 describes the concentration that produces the fitted 50% inhibitory effect. EC50 describes the concentration that produces the fitted 50% activation or efficacy response. This V1 calculator expects pre-normalized response data such as percent inhibition, percent activation, percent viability, or percent activity remaining.
Response = Bottom + (Top - Bottom) / (1 + 10^((LogEC50 - log10(Concentration)) x HillSlope))
The same 4-parameter logistic model is used for IC50 and EC50 analysis. In IC50 mode, the fitted log midpoint is reported as LogIC50; in EC50 mode, it is reported as LogEC50. Increasing and decreasing response directions are supported by the sign of the Hill slope.
Replicate response columns are averaged at each concentration, with SD and n reported in the results table. The fit uses unweighted concentration means and a client-side Levenberg-Marquardt nonlinear least-squares routine. Confidence intervals, weighted fitting, raw-control normalization, and multi-compound fitting are not included in V1.
Example Workflow
A scientist normalizes assay readouts, fits an IC50 or EC50 curve, reviews whether the potency estimate is trustworthy, and uses the recommended range to plan the next inhibitor or activator dilution series.
1
Normalize raw assay data to percent inhibition, percent activation, percent viability, or percent activity remaining.
2
Choose IC50 or EC50 analysis, select the response direction, and paste concentrations with optional replicate response columns.
3
Review the 4PL fit, graph, warnings, trust assessment, and recommended follow-up concentration range.
Common Mistakes
Using raw signal instead of normalized response
Normalize assay signal before fitting so the response scale matches the biological endpoint being interpreted.
Selecting the wrong analysis type
Use IC50 for inhibition workflows and EC50 for activation, agonist, efficacy, or reporter-response workflows.
Choosing the wrong response direction
Percent inhibition usually increases with dose, while percent viability or activity remaining usually decreases.
Not bracketing the 50% effect
Potency estimates are much more reliable when tested concentrations include responses below and above the fitted midpoint.
Using too few concentration points
Four levels is a hard minimum for a 4PL fit, but six or more concentrations are preferred for a trustworthy curve.
Mixing concentration units
Use one concentration unit for the pasted table and select that same unit before calculating.
Ignoring replicate variability
Large SD near the transition region can make IC50 or EC50 estimates unstable even when the curve looks plausible.
Over-trusting extrapolated values
IC50 or EC50 values outside the tested range should guide follow-up testing, not be treated as final potency estimates.
Frequently Asked Questions
What is an IC50?
IC50 is the concentration that produces the fitted 50% inhibitory effect in an inhibition assay.
What is an EC50?
EC50 is the concentration that produces the fitted 50% activation, efficacy, or response level in an activation assay.
What data should I paste into the calculator?
Paste pre-normalized concentration-response data with concentration in the first column and one or more response or replicate columns after it.
Do I need replicates?
No, but replicates help reveal noise. When replicate columns are provided, the calculator reports mean, SD, and n at each concentration.
What response direction should I choose?
Choose increasing response when the response rises with concentration. Choose decreasing response for viability or activity remaining data that falls with concentration.
Why does the calculator use a 4PL model?
A 4-parameter logistic model is a standard dose-response model that estimates lower plateau, upper plateau, midpoint, and Hill slope.
What does it mean if my IC50 or EC50 is outside the tested range?
The estimate is extrapolated beyond the data. Use it to plan a better concentration range, but interpret the value cautiously.
Is this equivalent to GraphPad Prism?
No. It uses client-side 4PL nonlinear least squares for practical planning, but it does not include Prism-style confidence intervals, weighting, constraints, or advanced diagnostics.