Date.h

#import <Foundation/Foundation.h>

@interface NSDate (Additions)

+ (instancetype)dateWithISO8601DateString:(NSString *)date;
+ (instancetype)dateWithISO8601DateTimeString:(NSString *)date;

@end

@interface NSDateFormatter (Additions)

+ (instancetype)ISO8601DateFormatter;
+ (instancetype)ISO8601DateTimeFormatter;

@end

Date.m

@implementation NSDate (Additions)

+ (instancetype)dateWithISO8601DateString:(NSString *)date {
    return [[NSDateFormatter ISO8601DateFormatter] dateFromString:date];
}
+ (instancetype)dateWithISO8601DateTimeString:(NSString *)date {
    return [[NSDateFormatter ISO8601DateTimeFormatter] dateFromString:date];
}

@end

@implementation NSDateFormatter (Additions)

+ (instancetype)ISO8601DateFormatter {
    static NSDateFormatter *fmt;
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        fmt = [[NSDateFormatter alloc] init];
        fmt.timeZone = [NSTimeZone timeZoneWithName:@"UTC"];
        fmt.dateFormat = @"yyyy-MM-dd";
    });
    return fmt;
}
+ (instancetype)ISO8601DateTimeFormatter {
    static NSDateFormatter *fmt;
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        fmt = [[NSDateFormatter alloc] init];
        fmt.timeZone = [NSTimeZone timeZoneWithName:@"UTC"];
        fmt.dateFormat = @"yyyy-MM-dd'T'HH:mm:ssZZZZZ";
    });
    return fmt;
}

@end