The percentage of false allegations of rape have varied across time due in part to the definition and the culture at the time of taking the measurement. Here’s one of latest, most cited studies on the issue. If you know of other peer-reviewed, independent studies, please share.
FALSE ALLEGATIONS OF RAPE: False Allegations of Sexual
Assault: An Analysis of Ten Years of Reported Cases
David Lisak, et. al (2010) Conclusion: false allegations of rape range from 2-8% http://www.icdv.idaho.gov/conference/handouts/False-Allegations.pdf