According to the debugger at http://regex101.com/ http://regex101.com/: /.*(\d)/ - Searches right-to-left, backtracking until it finds the match. /(\d)\D

According to the debugger at http://regex101.com/ http://regex101.com/: /.*(\d)/ - Searches right-to-left, backtracking until it finds the match. /(\d)\D*$/ - Searches left-to-right, going forward a step, backtrack, forward, backtrack, until it finds a match. If you're looking for a match toward the end of a string, the .* version will be faster.