Method and apparatus, including computer program products, implement techniques for quantifying a target nucleic acid (target) in a test sample. The techniques include providing a target and a defined initial amount of an internal control nucleic acid (control) different from the target; amplifying the target and control in a common amplification process; measuring a quantity indicating the amount of amplification product for the target and for the control in relation to a parameter representing the progress of the amplification; determining a characteristic value of the progress parameter for the target based on measurement results related to the amount of target amplification product; possibly determining a characteristic value of the progress parameter for the control based on measurement results related to the amount of control amplification product; and quantifying the original amount of target according to a predefined or selected quantification scheme using at least the characteristic value for the target.