 <p>There is no built-in NSString method available to do what you want. You need to write your own method. Objective-C does let you "extend" classes with new methods to cover cases like this. </p> <p>This is how I would do it:</p> <pre><code>@interface NSString(Extend) -(NSInteger)proximity:(NSString*)otherString; @end @implementation NSString(Extend) -(NSInteger)proximity:(NSString*)otherString { NSUInteger length = [otherString length]; if(length != [self length]) return -1; NSUInteger k; NSUInteger differences = 0; for(k=0;k&lt;length;++k) { unichar c1 = [self characterAtIndex:k]; unichar c2 = [otherString characterAtIndex:k]; if(c1!=c2) { ++differences; } } return differences; } @end </code></pre> <p>Then in my code at the place I wanted to check I would say something like</p>