The present invention provides method of quantifying sample clean up in real time by providing curve-fitting measurements of optical or physical properties of fluid samples in boreholes. Sample fluid is extracted from the formation surrounding the borehole. As fluid continues to be extracted the composition of the extracted sample changes, altering the values of physical properties of the sample being measured. Measurements are made of optical or physical properties of the sampled fluid, and regression analysis is performed on the acquired measured data points. In one embodiment of the invention, iterative methods enable a user to determine an asymptotic value of a physical property, i.e. absorbance, as well as the percent of the progress that the current sample has obtained toward reaching the asymptotic property value and a projected time to reach the asymptotic property value. If the projected time required to reach that asymptotic value is too long, the operator may decide to abandon extracting fluid from the region. In another embodiment, a more general method enables the user to estimate, through the value of a variable, the speed at which cleanup can occur. The physical properties of the sample may be fit as a function of pumping time or volume.