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qPCR Calculator

qPCR relative fold-change from Ct values and efficiency.

Introduction

qPCR Calculator — qPCR relative fold-change from Ct values and efficiency. Enter Control Ct, Sample Ct, Amplification efficiency (0-1) to get an instant, accurate result.

Formula

Relative fold change between a control and sample = (1 + E)^(Ct_control − Ct_sample), a Livak-style ΔCt comparison using an assumed amplification efficiency E (this simplified version does not additionally normalize against a reference/housekeeping gene, unlike the full ΔΔCt method).

Step-by-step

  1. Enter the Control Ct.
  2. Enter the Sample Ct.
  3. Enter the Amplification efficiency (0-1).
  4. Click Calculate to see your result instantly.

Real-world example

Example: With Control Ct = 20, Sample Ct = 17, Amplification efficiency (0-1) = 1, the qPCR Calculator gives Fold Change: 8.

Frequently Asked Questions

What does a lower Ct value mean?
A lower cycle threshold (Ct) means the target reached detectable amplification sooner, which indicates a higher starting template quantity in that sample.
Is this the same as the full ΔΔCt method?
It captures the core exponential relationship between Ct difference and fold change, but the complete ΔΔCt method also normalizes both control and sample against a stable reference gene — factor that in separately if you need fully normalized results.
What inputs does the qPCR Calculator need?
You'll need to provide: Control Ct, Sample Ct, Amplification efficiency (0-1). All fields use sensible defaults, so you can see a working example immediately and then adjust the values to match your own numbers.
How accurate is the qPCR Calculator?
The qPCR Calculator applies the formula exactly as calculated — Relative fold change between a control and sample = (1 + E)^(Ct_control − Ct_sample), a Livak-style ΔCt comparison using an assumed amplification efficiency E (this simplified version does not additionally normalize against a reference/housekeeping gene, unlike the full ΔΔCt method). — so results are precise for the inputs you provide. Accuracy depends on entering correct, realistic input values.
Is the qPCR Calculator free to use?
Yes, the qPCR Calculator is completely free, requires no signup, and runs instantly in your browser.

About the qPCR Calculator

The qPCR Calculator uses a real, verifiable formula — Relative fold change between a control and sample = (1 + E)^(Ct_control − Ct_sample), a Livak-style ΔCt comparison using an assumed amplification efficiency E (this simplified version does not additionally normalize against a reference/housekeeping gene, unlike the full ΔΔCt method). — so results are accurate every time, not an approximation.