An assay device for the quantitative determination of an analyte, comprising a test strip containing 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, (a) said test membrane containing a test site having immobilized thereon a ligand capable of reacting with the analyte and binding such to the test site, and two standard band sites having immobilized thereon known high and low concentrations of a calibrator agent capable of reacting with a label conjugate and binding such to the standard sites, a first standard band site having immobilized thereon a high concentration of a first calibrator agent corresponding to a known concentration of analyte, a second standard band site having immobilised thereon a different low concentration of a second calibrator agent corresponding to a known concentration of an analyte, wherein standard band sites are capable of reacting with separate label conjugates for each calibrator agent and binding such the standard sites and giving rise to a measurable response, and wherein the two calibrator agents are in separate standard sites, before and after the test site, (b) said upstream membrane having a site for the application of a sample to be analyzed and having a site downstream from the sample application site for depositing label conjugates capable of reacting with the analyte and label conjugates capable of reacting with the immobilized calibrator agents in the standard bands to provide a known label response in the standards bands, and (c) said downstream membrane capable of absorbing said sample and providing the capillary flow for the sample through the upstream and test membrane. (a) said test membrane containing a test site having immobilized thereon a ligand capable of reacting with the analyte and binding such to the test site, and two standard band sites having immobilized thereon known high and low concentrations of a calibrator agent capable of reacting with a label conjugate and binding such to the standard sites, a first standard band site having immobilized thereon a high concentration of a first calibrator agent corresponding to a known concentration of analyte, a second standard band site having immobilised thereon a different low concentration of a second calibrator agent corresponding to a known concentration of an analyte, wherein standard band sites are capable of reacting with separate label conjugates for each calibrator agent and binding such the standard sites and giving rise to a measurable response, and wherein the two calibrator agents are in separate standard sites, before and after the test site, (b) said upstream membrane having a site for the application of a sample to be analyzed and having a site downstream from the sample application site for depositing label conjugates capable of reacting with the analyte and label conjugates capable of reacting with the immobilized calibrator agents in the standard bands to provide a known label response in the standards bands, and (c) said downstream membrane capable of absorbing said sample and providing the capillary flow for the sample through the upstream and test membrane.