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qPCR ΔΔCt Calculator: relative gene expression (fold change) from Ct values

37degrees Team
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qPCR ΔΔCt Calculator: relative gene expression (fold change) from Ct values

Fold change without the spreadsheet

The ΔΔCt method is the standard for relative qPCR quantification — but it’s fiddly to set up every time. Paste your Ct values, mark the control, and get ΔCt, ΔΔCt, and fold change with a bar chart.

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What it does

  • Editable sample table — target Ct + reference (housekeeping) Ct per sample. Cells accept comma-separated replicate Cts and average them.
  • Pick the calibrator — mark the control row; everything is reported relative to it.
  • ΔCt → ΔΔCt → fold — Fold = 2^−ΔΔCt (Livak), with an optional amplification-efficiency input (the base becomes 1 + efficiency%/100).
  • Bar chart — log₂ fold change per sample (induced above the line, repressed below), with the fold value labelled.

The method

ΔCt = Ct(target) − Ct(reference), ΔΔCt = ΔCt(sample) − ΔCt(calibrator), fold = 2^−ΔΔCt. Example: a control at 25.0/18.0 (target/GAPDH), Treatment A at 23.5/18.1 → 3.0× up, Treatment B at 26.8/18.0 → 0.29× (down).

The Livak method assumes target and reference amplify at ~100% efficiency. For very different efficiencies, the Pfaffl method (separate per-gene efficiencies) is more accurate — the single global efficiency here is a first-order correction.

Embed it on your site

<link rel="stylesheet" href="https://www.37degrees.io/interactive-tools/qpcr-ddct/styles.css" />

<div id="qpcr-widget-embed"></div>

<script>
  // Optional: window.QPCR_THEME = "light";
</script>
<script src="https://www.37degrees.io/interactive-tools/qpcr-ddct/widget.js"></script>

Credits

Built and maintained by 37degrees. Livak & Schmittgen (2001) ΔΔCt method — no third-party libraries, no data leaves the browser.

Frequently asked questions

Is there a free qPCR ddCt calculator?
Yes. The 37degrees qPCR ΔΔCt Calculator is free and browser-based. Enter target and reference Ct values per sample, mark the calibrator, and get ΔCt, ΔΔCt, and 2^−ΔΔCt fold change with a bar chart. Replicate Cts are averaged automatically.
What is the ΔΔCt (Livak) method?
The ΔΔCt method, described by Livak and Schmittgen in 2001, calculates relative gene expression from qPCR. You normalize each target Ct to a reference (housekeeping) gene to get ΔCt, compare against a calibrator sample to get ΔΔCt, then take 2 to the power of negative ΔΔCt as the fold change.
How do I calculate fold change from Ct values?
Subtract the reference Ct from the target Ct for each sample to get ΔCt, subtract the calibrator's ΔCt to get ΔΔCt, then raise 2 to the power of negative ΔΔCt. The result is the fold change in expression relative to the calibrator.
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