This article describes a numerical approach, which allows for the analysis of the residence time distribution (RTD) in microchannels. While the traditional methods provide the RTD at the outlet of the reactor, we consider the distribution of the tracer's age across the entire flowfield. The equation for the tracer's age distribution is solved by a modified method of moments and the distribution function is calculated by a reconstruction procedure. As at, example we consider a Dean vortex-based micromixer. (C) 2010 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.