NSDate Min and Max Possible Values

Question

Anyone know what the minimum and maximum possible values are for an NSDate?

Answer 1

Use [NSDate distantFuture] and [NSDate distantPast].

Answer 2

EDITED Answer:

I thought that I'd discovered the minimum date value was 0001-01-01 00:00:00 + 0000 (given my code below) HOWEVER as has been pointed out in the comments below, this is only for the current era (i.e. A.D.). An NSDate value can go lower than this but what you see as a result of an NSLog may not be what you are expecting, so I would recommend looking at other answers here and ignoring my ignorance.

ORIGINAL Answer:

I believe that I've discovered the minimum date value is 0001-01-01 00:00:00 + 0000

You need to be very careful when NSLog'ing and parsing values to ensure that your timezone isn't skewing the date value slightly.

I will try and demonstrate below:

NSDateFormatter *dateFormatter1 = [[NSDateFormatter alloc] init];
[dateFormatter1 setDateFormat:@"yyyy-MM-dd hh:mm:ss z"];

NSDateFormatter *dateFormatter2 = [[NSDateFormatter alloc] init];
[dateFormatter2 setDateFormat:@"yyyy-MM-dd HH:mm:ss z"];

NSDateFormatter *dateFormatter3 = [[NSDateFormatter alloc] init];
[dateFormatter3 setDateFormat:@"yyyy-MM-dd HH:mm:ss z"];
[dateFormatter3 setTimeZone:[NSTimeZone timeZoneForSecondsFromGMT:0]];

NSDate *date1 = [NSDate dateWithTimeIntervalSince1970:-62135596800];
NSLog(@"date1 = %@", date1);
NSLog(@"date1 via dateFormatter1 = %@", [dateFormatter1 stringFromDate:date1]);
NSLog(@"date1 via dateFormatter2 = %@", [dateFormatter2 stringFromDate:date1]);
NSLog(@"date1 via dateFormatter3 = %@", [dateFormatter3 stringFromDate:date1]);

NSDate *date2 = [NSDate dateWithTimeIntervalSince1970:-62135596800 - 100]; // The - 100 makes no difference
NSLog(@"date2 = %@", date2);
NSLog(@"date2 via dateFormatter1 = %@", [dateFormatter1 stringFromDate:date2]);
NSLog(@"date2 via dateFormatter2 = %@", [dateFormatter2 stringFromDate:date2]);
NSLog(@"date2 via dateFormatter3 = %@", [dateFormatter3 stringFromDate:date2]);

This results in the following output (on my iPad given its particular timezone):

date1 = 0001-01-01 00:00:00 +0000
date1 via dateFormatter1 = 0001-12-31 11:58:45 GMT-00:01:15
date1 via dateFormatter2 = 0001-12-31 23:58:45 GMT-00:01:15
date1 via dateFormatter3 = 0001-01-01 00:00:00 GMT
date2 = 0001-12-31 23:58:20 +0000
date2 via dateFormatter1 = 0001-12-31 11:57:05 GMT-00:01:15
date2 via dateFormatter2 = 0001-12-31 23:57:05 GMT-00:01:15
date2 via dateFormatter3 = 0001-12-31 23:58:20 GMT

Note date2 and how subtracting an additional 100 seconds did not reduce the value of the date but actually seemed to increase it. Obviously something peculiar about the way the internals of NSDate work, the time is adjusted by 100 seconds but this skews the day and month perhaps because it couldn't go any lower?

Answer 3

maximum should be: 5828963-12-20 00:00:00 +0000 because

NSDate *dateSinceNow = [NSDate dateWithTimeIntervalSinceNow:DBL_MAX];
NSDate *dateSindeReferenceDate = [NSDate dateWithTimeIntervalSinceReferenceDate:DBL_MAX];
NSLog(@"min: %@, max: %@", dateSinceNow, dateSindeReferenceDate);

is the same.

minimum i get this is: 0001-01-01 00:00:00 +0000

cause this is what i get when i try:

NSDateFormatter *df = [[NSDateFormatter alloc] init];
[df setDateFormat:@"yyyy-MM-dd hh:mm:ss"];
[df setTimeZone:[NSTimeZone timeZoneForSecondsFromGMT:0]];
NSDate *myDate = [df dateFromString: @"0001-01-01 00:00:00"];
NSLog(@"%@", myDate);

but this is current era as pointed out by davedelong

so if you try the first example with - DBL_MAX you get: 41221-07--2147483641 00:00:00 +0000. no idea what era this is...

Answer 4

The OP's real question (clarified in his comment to his own OP) is about 1/1/1. As you can see from the Playground below in my TL;DR;, Apple prints "31 Dec 0001" instead of "31 Dec 0001 BC" if you don't specify a DateFormatter with Era, so 1/1/1 AD could easily be 31/1/1 BC (the day before) if the OP's local timezone wasn't UTC.

NSDate / Date can effectively be used up to ~30m years in the past, but NSDateComponents / DateComponents operations fail with dates before 4500 BC. Read on for details...

TL;DR;

As some commentators and respondents have pointed out, [NSDate distantPast] (or Date.distantPast in Swift) is supplied by the API, however, that is not the minimum NSDate / Date - it is simply a convenience for business logic, since few applications need to do calculations into BCE (note that .distantFuture is also arbitrary - it's 1st January 4001 AD).

Other respondents (@peko) have dealt with real "distantFuture" maxima, but no one has fully explored the minimum.

So what does Date do when you actually give it dates before .distantPast? Here's a wee Playground:

// Swift 5 Playground
import Foundation

var d = Date.distantPast // "31 Dec 1 at 23:58"
// However, that's the default print, which *does not* include Era

let df = DateFormatter()
df.dateFormat = "EEEE dd MMMM yyyy G" // "G" is Era

print(df.string(from: d)) // "Friday 31 December 0001 BC\n"

// What happens when we go lower?
d = d.addingTimeInterval(-1e12) // "29 Nov 31689 at 22:12"
print(df.string(from: d)) // Thursday 29 November 31689 BC\n"

// Lower still?
d = d.addingTimeInterval(-1e14) // "18 Feb 3200497 at 12:25"
print(df.string(from: d)) // "Tuesday 18 February 3200497 BC\n"

// But it breaks here...
d = d.addingTimeInterval(-1e15) // ""
print(df.string(from: d)) // "\n"

So NSDate / Date has an effective minimum ~30m years in the past.

I have, however, had difficulty in doing calculations in much more recent times than NSDate / Date can deal with.

Specifically, Calendar's .dateComponents(unitFlags, from: date) fails (and prints an error message like below), earlier than about 4713 BC.

2021-12-03 19:15:48.885955+0000 Tempus II[61381:6027263] [general] CFAbsoluteTime -268229356861.914001 exceeds calendar calculation range.

... that "-268229356861.914001" is 6500 BC, but any trying to do DateComponent calculations on anything before 4713 BC will give a similar message, and the calculations will be wrong!

Here's another wee Playground to try that yourself:

let df = DateFormatter()
df.dateFormat = "EEEE dd MMMM yyyy G" // "G" is Era

// 500BC -> by 1000 years, which works
let dc500 = DateComponents(calendar: .autoupdatingCurrent,
                           era: 0,
                           year: 500)
var d = Calendar.autoupdatingCurrent.date(from: dc500)!
print(df.string(from: d)) // Thursday 01 January 0500 BC\n"

d = Calendar.autoupdatingCurrent.date(byAdding: delta, to: d)!
print(df.string(from: d)) // "Monday 01 January 0501 AD\n"
// *** NB 501AD is the RIGHT answer for 500BC + 1000, as there
// *** was no year 0

d = Calendar.autoupdatingCurrent.date(byAdding: delta, to: d)!
print(df.string(from: d)) // "Friday 01 January 1501 AD\n"


// 5000BC -> by 2000 years, which doesn't work
delta = DateComponents(calendar: .autoupdatingCurrent,
                       year: 2000)

let dc5000 = DateComponents(calendar: .autoupdatingCurrent,
                            era: 0,
                            year: 5000)
d = Calendar.autoupdatingCurrent.date(from: dc5000)!
print(df.string(from: d)) // "Sunday 01 January 5000 BC\n"

d = Calendar.autoupdatingCurrent.date(byAdding: delta, to: d)!
print(df.string(from: d)) // "Tuesday 01 January 2713 BC\n"
// *** WRONG!

d = Calendar.autoupdatingCurrent.date(byAdding: delta, to: d)!
print(df.string(from: d)) // "Wednesday 01 January 0713 BC\n"
// *** Back on track again

d = Calendar.autoupdatingCurrent.date(byAdding: delta, to: d)!
print(df.string(from: d)) // "Thursday 01 January 1288 AD\n"
// *** Again, correct 
// 713 -> 1BC + 1 AD -> 1288 = 1288 + 713 - 1 = 2000

p.s.

Don't use Date in business logic without understanding TimeZone, Calendar, DateComponents and DateFormatter!