The accuracy of carbon-14 dating depends on a variety of factors. Obtaining a good sample is one. Artifacts are easily contaminated with "current"carbon from the environment. Several samples need to be examined. The method also relies on the assumption that the rate of cosmic ray bombardment has not varied much over the useful range of C-14 dating.

This used to be a major bone of contention among critics of the process. Studies of tree growth-rings have revealed uneven cosmic ray bombardments during some periods of the time frame accessible to C-14 dating (about 24,000 years). This is now taken into account in current work.