Scenario
You have sample and control Ct values for target and reference genes.
The example shows the sequence from raw Ct to fold-change, including where interpretation can still go wrong.
Inputs to confirm
Target and reference Ct values for both sample and control.
Whether the reference gene is actually stable in the relevant biological context.
Whether replicate spread is acceptable before summarizing the result.
Why this page adds value
The calculator provides the answer quickly, but the example teaches when not to trust the answer.
That distinction is often what makes the page useful to a real lab rather than just to search crawlers.
Common failure points
Using an unstable reference gene.
Ignoring high Ct values near the assay detection limit.
Treating fold-change as meaningful before checking replicate consistency.