Defensive Gun Use DGU is actually an unsettled frontier in research.
Defensive gun use surveys USA and counts of DGU incidents per year:
Government:
NCVS 108,000
NSPOF (raw) 23,000,000
NSPOF (vetted) 4,700,000
Private sector:
Kleck-Gertz 2,400,000
Lott 2,100,000
About thirteen or so other surveys 700,000 to 3,600,000 per year.
All these results depend on how the survey sample was selected, how large a sample was used, how the questions were presented to the respondents, and so on. One of the raw NSPOF respondents (dropped from the vetted subsample) was a lady who claimed to use a gun defensively 52 times a year.
NCVS asked Have you been a victim of a crime? If yes, then Did you resist? If yes, then How did you resist? Very low number of DGU.
NSPOF asked all of the 2568 sample, have you used a gun to defend yourself in the past year? Very high number of DGU. Of the final, vetted subsample of DGU respondents (19 out of 2568) six did not consider themselves crime victims. If those folks had been surveyed by NCVS protocol, they would not have been asked if they had defended themselves with a gun.
Remember too that the DGUser was responding to a perceived threat. How many were actually crimes as counted by FBI UCR is hard to guess. One of Kleck's surveys projected that 400,000 DGUsers believed they saved their life or the life of a third party; if only 10% were correct in their belief, that would be 40,000 lives saved.