Albert Barnes Commentary Judges 20:46

"So that all who fell that day of Benjamin were twenty and five thousand men that drew the sword; all these [were] men of valor." — Judges 20:46 (ASV)

In Judges 20:35, the number given is 25,100. Judges 20:44–46 give the details of the loss on that day: 18,000, 5,000, and 2,000; in all 25,000. But as the Benjamites numbered 26,700 men (Judges 20:15), and 600 escaped to the rock of Rimmon, it is clear that 1,100 are unaccounted for, partly from no account being taken of those who fell in the battles of the first two days, partly from the use of round numbers, or from some other cause. The numbers given both here and in Judges 20:35 are expressly restricted to those who fell on "that" (the third) "day."