How can I predict the percent qPCR signal due to contaminating DNA, for a given qPCR assay, and its matching NRT control?
FAQ ID -2688

Assuming 100% amplification efficiency, each step increase in Ct value represents a doubling in the amount of qPCR template. Therefore, evaluating the difference in Ct values between the qPCR assay, and its matching NRT control, leads to the following predictions:

CtNRT - Ct+RT Fraction of gene expression signal due to contaminating DNA Percentage of gene expression signal due to contaminating DNA
1 (1/21) = 1/2 50%
2 (1/22) = 1/4 25%
3 (1/23) = 1/8 13%
4 (1/24) = 1/16 6%
5 (1/25) = 1/32 3%