The present invention relates to a quantitative assay device and a method for the determination of an analyte, based on a test strip, which contains a porous test membrane allowing for capillary flow of the analyte and complexes of the analyte, a porous upstream membrane in fluid connection with the test membrane and a porous downstream membrane in fluid connection with the test membrane, wherein the test membrane contains two bands having deposited on there high and low concentrations of different calibrator agents and a test band capable of reacting with conjugated analyte complexes giving rise to a measurable signal.