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Carbonless copy paper has been used extensively in many fields in China since 1990s. Document examiners were often requested to confirm the authenticity of questioned carbonless copy documents. Estimating the age of carbonless copy documents could be an effective method to confirm the authenticity of such documents. Estimating age is an important and difficult problem, and is also an important task that forensic document examiners should confront. In this paper, a fading rate method was successfully employed to estimate the relative age of carbonless copy documents by comparing fading rates. Using extensive tests, butanol proved to be a suitable solvent and was used to dissolve and fade the dye of carbonless copy line strokes made at different times. The relative age of the line strokes was estimated by means of changing rate of gray value. As preliminary findings of this study, curves were created to indicate the relationship between the fading rate (changing rate of gray value) of line strokes and the age of carbonless copy documents. It was also determined that the amount of solvent, brands of carbonless copy paper and thickness of carbonless copy line strokes had varying impacts on estimating the dates of carbonless copy line strokes. Experimental results showed that the fading rate method was applicable for finding the relative age of questioned carbonless copy documents in some cases where the strokes were produced on the document within 43 months. [ABSTRACT FROM AUTHOR]