There are two contradictory traditions relating the number of males that left Egypt in the Exodus. The older Elohist tradition relates that there were 600,000. This number is revised upward by the later Priestly writer to 625,550.
The reason for this revision is unclear. Perhaps the Priestly writer fabricated it in order to lend verisimilitude to the earlier tradition’s too round of a number. Another Priestly text tells us that there were 603,550 non-Levite males (Ex 38:26) and 22,000 Levite males (Num 3:39), thus totaling 625,550.
In either case, just as there were 400 years of captivity in the earlier sources and 430 in the Priestly version (#32), so too here with the earlier 600,000 and P’s 625,550.
In Exodus 12:37 is says “about“ six hundred thousand.