# ConductScience qPCR ΔΔCt Calculator: method and validation record

This record fixes the calculation behind the free qPCR ΔΔCt Calculator at https://conductscience.com/tools/qpcr-ddct-calculator, and the worked examples that check it.

## What the tool computes

From Ct values for one or more target genes and one or more reference genes, per sample:

- mean Ct per sample and gene, after dropping outlying replicates;
- ΔCt = mean target Ct − mean reference Ct;
- ΔΔCt = ΔCt of the sample − mean ΔCt of the control samples;
- fold change = 2^−ΔΔCt and log2 fold change = −ΔΔCt.

Input is pasted `Sample, Gene, Ct` rows or an RDML file. Blank and undetermined Ct values are excluded.

## Files

| File | Contents |
| --- | --- |
| `METHODS.md` | Formulas, the outlier rule, conventions, references, and changes from the page before this record |
| `cases.json`, `cases.csv` | The worked examples: inputs, expected outputs and where each expected answer comes from |
| `validation-report.json` | The engine's output for every case, pass or fail, and the SHA-256 of each engine file |
| `engine/` | The calculation source files the report fingerprints (when included) |
| `data_dictionary.csv` | Columns of `cases.csv` |
| `CITATION.cff`, `LICENSE`, `MANIFEST.json` | Citation metadata, licence, and byte count and SHA-256 of every file |

## How to cite

ConductScience. ConductScience qPCR ΔΔCt Calculator [software]. 2026. https://doi.org/10.55157/csd.tool.qpcrddct.2026.001

In a methods section: "Relative expression was calculated with the 2^−ΔΔCt method (Livak and Schmittgen, 2001) using the ConductScience qPCR ΔΔCt Calculator (https://doi.org/10.55157/csd.tool.qpcrddct.2026.001)."