Free AI-Assisted

IC50 Calculator

Batch-fit IC50 and EC50 from one CSV with QC flags—free, no account. Built-in AI agent assistant support.

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Key facts

Key facts about IC50 Calculator
FactValue
InputsCSV paste or upload: compound ID, concentration, response (auto-detected column names)
Models4PL, 5PL, or Auto (F-test selects best)
IC50 typesAbsolute (free Top/Bottom + optional constraints) or Relative (Top=100, Bottom=0)
Regression weightingUnweighted, 1/Y, or 1/Y²
OutputsIC50, EC50, Hill slope, R², pIC50, EC10, EC90; Good fit / Review / Poor fit badge
Min data points4 per compound; zero concentration excluded from log-scale fit
Bootstrap CI95% CI ribbon (500 iterations) in curve inspector
ExportsExport All CSV, Methods PDF, Share link, per-curve SVG/PDF
File limit5 MB CSV upload warning
Runs in browserYes — no install; data stays local
Account requiredNo

What it does

Fitting dose-response curves compound by compound in desktop software wastes hours on HTS screens—and a converged fit with no plateau warning can still produce a misleading IC50. The IC50 Calculator accepts a multi-compound CSV from a plate reader, fits every curve in one step, and flags unreliable results before you paste values into a SAR table.

Paste or upload a CSV with concentration, response, and compound ID columns—or click Load example data to explore the workflow. Set Model (4PL, 5PL, or Auto with F-test), IC50 type (absolute or relative Top=100/Bottom=0), Regression weighting, and optional Top/Bottom constraints. Click Run Fit; the Results table lists IC50, EC50, Hill slope, R², pIC50, EC10, and EC90 with a fit-quality badge per compound. Click any row to open the curve inspector with a 95% bootstrap CI ribbon; click outlier points to exclude them, then Run Fit again. Download Export All CSV, Methods PDF, Share link, or per-curve Export SVG / Export PDF.

Why researchers use it

  • Fit an entire HTS plate from one CSV upload
  • Catch unreliable IC50 when plateaus are missing
  • Avoid one-curve-at-a-time desktop workflows
  • Export SAR tables with pIC50 and EC10/EC90
  • Share exact analyses via permalink with collaborators
  • Keep screen data local—no account or install

Best for

  • HTS and dose-response inhibitor screens
  • Kinase and receptor potency panels
  • SAR tables needing pIC50 values
  • Teaching pharmacology without paid licenses
  • Reviewer requests for reproducible curve parameters
  • Quick QC before formal statistical analysis

When to use this vs alternatives

Choose this tool when you need batch IC50/EC50 from a plate-reader CSV with QC flags, curve inspection, and export in one browser session. Use the Serial Dilution Planner when you are planning pipette-ready dose dilutions before the screen runs. Use the Absorbance Curve Calculator when you need sample concentrations from a standard curve—not multi-compound potency fitting. GraphPad Prism and R (drc) still fit if you already have a trusted single-curve or scripted pipeline.

What makes it different

Most alternatives excel at single-curve fitting or scripting—but not batch QC grading with plain-English warnings in a free browser workflow. GraphPad Prism costs hundreds per year and fits one compound at a time. ConductScience's free IC50 calculator handles a single curve with no batch dashboard. R packages like drc automate batch fitting but require scripting and cryptic error messages.

This calculator fits every compound from one CSV upload, grades each fit with traffic-light QC badges and plain-English reasons, auto-selects 4PL vs 5PL when set to Auto, and exports SAR-ready CSV plus vector figures—free in the browser with data staying on your machine. Researchers switch when fitting dozens of compounds one by one is impractical or when convergence failures produce IC50 values with no warning.

How to get started

  1. Open the workspace on the Fit tab; paste CSV data or click Load example data.
  2. Set Model, IC50 type, and Regression weighting; add Top/Bottom constraints if using absolute IC50.
  3. Confirm the green Ready to fit strip; click Run Fit.
  4. Review the Results table and Curve preview; click a compound row to inspect the curve.
  5. Click outlier points to exclude them if needed; click Run Fit again.
  6. Click Export All CSV, Methods PDF, Share link, or per-curve Export SVG / Export PDF.

Frequently asked questions

What is the difference between relative and absolute IC50?
Relative IC50 constrains the curve between Top=100 and Bottom=0—standard for normalized inhibition or viability data. Absolute IC50 fits free Top and Bottom plateaus and reports the concentration at 50% of the fitted response range—better when raw signal units matter. Choose IC50 type in Model settings; optional Top/Bottom constraints apply in absolute mode.
What is pIC50 and when do I use it?
pIC50 is the negative base-10 logarithm of IC50 in molar units (e.g. IC50 = 100 nM → pIC50 ≈ 7.0). Medicinal chemists use pIC50 in SAR tables because higher values mean greater potency. This calculator outputs pIC50 alongside IC50 in the results table and CSV export.
Should I use 4PL, 5PL, or Auto?
4PL fits sigmoidal dose-response with Top, Bottom, IC50, and Hill slope—adequate for most screens. 5PL adds an asymmetry parameter for uneven plateaus. Auto runs an F-test and picks the better model per compound. Start with Auto unless your protocol requires a fixed model.
When should I not trust an IC50 value?
Do not trust IC50 when the fit badge shows Poor fit (red) or Review (amber). Common reasons: fewer than four data points, flat response, convergence failure, R² below 0.90, plateau not reached, or extreme Hill slope. The curve inspector lists plain-English QC messages. Exclude outlier points and Run Fit again—or constrain Top/Bottom if you know assay limits.
How do I format CSV for batch IC50 fitting?
Use three columns: compound ID, concentration, and response. Header names are flexible—the tool recognizes aliases like conc, dose, inhibition, and compound. Concentrations can include units (nM, µM, pM). One row per concentration per compound; duplicates are averaged. Excel: save as CSV or copy-paste. Minimum four concentration points per compound.
Do I need an account to save or share an analysis?
No. Share link encodes the dataset and model settings in the URL. Recent runs appear on the History tab (up to five saved in your browser). Export All CSV and Methods PDF give offline records for notebooks and manuscripts.

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Last updated . Pepkio builds free lab calculators alongside bioinformatics CRO services.