I have a time interval that spans years and I want all the time components from year down to seconds.

My first thought is to integer divide the time interval by seconds in a year, subtract that from a running total of seconds, divide that by seconds in a month, subtract that from the running total and so on.

That just seems convoluted and I've read that whenever you are doing something that looks convoluted, there is probably a built-in method.

Is there?

I integrated Alex's 2nd method into my code.

It's in a method called by a UIDatePicker in my interface.

NSDate *now = [NSDate date];
NSDate *then = self.datePicker.date;
NSTimeInterval howLong = [now timeIntervalSinceDate:then];

NSDate *date = [NSDate dateWithTimeIntervalSince1970:howLong];
NSString *dateStr = [date description];
const char *dateStrPtr = [dateStr UTF8String];
int year, month, day, hour, minute, sec;

sscanf(dateStrPtr, "%d-%d-%d %d:%d:%d", &year, &month, &day, &hour, &minute, &sec);
year -= 1970;

NSLog(@"%d years\n%d months\n%d days\n%d hours\n%d minutes\n%d seconds", year, month, day, hour, minute, sec);

When I set the date picker to a date 1 year and 1 day in the past, I get:

1 years 1 months 1 days 16 hours 0 minutes 20 seconds

which is 1 month and 16 hours off. If I set the date picker to 1 day in the past, I am off by the same amount.

Update: I have an app that calculates your age in years, given your birthday (set from a UIDatePicker), yet it was often off. This proves there was an inaccuracy, but I can't figure out where it comes from, can you?