DateTime.Compare how to check if a date is less than 30 days old?

Question

I'm trying to work out if an account expires in less than 30 days. Am I using DateTime Compare correctly?

if (DateTime.Compare(expiryDate, now) < 30)

{
     matchFound = true;
}

Konrad Rudolph · Accepted Answer · 2022-11-02T14:06:21.747

261

Am I using DateTime Compare correctly?

No. Compare only offers information about the relative position of two dates: less, equal or greater. What you want is something like this:

if ((expiryDate - DateTime.Now).TotalDays < 30)
    matchFound = true;

This subtracts two DateTimes. The result is a TimeSpan object which has a TotalDays property.

Additionally, the conditional can be written directly as:

bool matchFound = (expiryDate - DateTime.Now).TotalDays < 30;

No if needed.

Alternatively, you can avoid naked numbers by using TimeSpan.FromDays:

bool matchFound = (expiryDate - DateTime.Now) < TimeSpan.FromDays(30);

This is slightly more verbose but I generally recommend using the appropriate types, and the appropriate type in this case is a TimeSpan, not an int.

edited Nov 02 '22 at 14:06

answered Feb 09 '09 at 14:39

Konrad Rudolph

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Should be allowed to give you 2+ ;) one for the answer and one for the short way to express it – CheGueVerra Feb 09 '09 at 14:40
4

Uh … I just made my answer longer so feel free to subtract one imaginary vote. ;-) – Konrad Rudolph Feb 09 '09 at 14:42
1

Please use [`TotalDays`](http://msdn.microsoft.com/en-us/library/system.timespan.totaldays.aspx) instead of days. – João Portela Feb 20 '13 at 10:40
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@João Why? It makes no difference in this case. – Konrad Rudolph Feb 20 '13 at 10:51
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It is conceptually more accurate. It makes no difference because `Days` is the biggest component of `TimeSpan`. People reading this can extrapolate that to think that the `Seconds` property works the same way. – João Portela Feb 20 '13 at 11:33
1

@João Hmm. Agreed. Will change. – Konrad Rudolph Feb 20 '13 at 11:34
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Adding to the point João Portela made, even `Days` itself can be wrong too. `Days` and `TotalDays` are the same here only because the condition is `< 30`, but there would be an obvious difference if it was `<= 30`, because `TotalDays` may returns something like `30.421` while `Days` still returns `30`. – Racil Hilan Apr 16 '14 at 16:37
Thank you ... it helped me a lot. – Thiago Cunha Jan 31 '19 at 19:39

score 16 · Answer 2 · answered May 25 '10 at 06:40

16

should be

matchFound = (expiryDate - DateTime.Now).TotalDays < 30;

note the total days otherwise you'll get werid behaviour

answered May 25 '10 at 06:40

Luke

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this answer was over a year after the last edit to accepted answer! – Mitch Wheat Jan 12 '13 at 01:23
@Mitch - This is the correct answer, notice he is using TotalDays rather than Days. – Marcelo Mason Jan 20 '13 at 22:42
The accepted answer is correct. TotalDays returns a fractional portion as well, which is redundant when comparing to an integer. – Mitch Wheat Jan 20 '13 at 23:57
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@MitchWheat `TotalDays` is **conceptually** correct field to use. In practice they give the same result but only because `Days` is the biggest component of `TimeSpan`, had there been a Months or Years component and this would have been a different story. Just try with `Hours`, `Seconds` or `Milliseconds` to see how they work. – João Portela Feb 20 '13 at 10:40

score 7 · Answer 3 · answered Feb 09 '09 at 14:45

7

Well I would do it like this instead:

TimeSpan diff = expiryDate - DateTime.Today;
if (diff.Days > 30) 
   matchFound = true;

Compare only responds with an integer indicating weather the first is earlier, same or later...

answered Feb 09 '09 at 14:45

haqwin

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JaredPar · Answer 4 · 2009-02-09T15:14:28.910

5

Try this instead

if ( (expiryDate - DateTime.Now ).TotalDays < 30 ) { 
  matchFound = true;
}

edited Feb 09 '09 at 15:14

answered Feb 09 '09 at 14:40

JaredPar

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Hmm, you need to either invert the order of your dates or take the absolute value, unless the expiration date is already passed. – Konrad Rudolph Feb 09 '09 at 14:45

Mitch Wheat · Answer 5 · 2013-01-12T01:21:02.920

3

Compare returns 1, 0, -1 for greater than, equal to, less than, respectively.

You want:

    if (DateTime.Compare(expiryDate, DateTime.Now.AddDays(30)) <= 0) 
    { 
        bool matchFound = true;
    }

edited Jan 12 '13 at 01:21

answered Feb 09 '09 at 14:44

Mitch Wheat

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Magic Mick · Answer 6 · 2019-09-03T04:10:03.047

1

Assuming you want to assign false (if applicable) to matchtime, a simpler way of writing it would be..

matchtime = ((expiryDate - DateTime.Now).TotalDays < 30);

edited Sep 03 '19 at 04:10

answered Feb 18 '15 at 01:54

Magic Mick

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The ternary operator here is completely redundant as ((expiryDate - DateTime.Now).TotalDays < 30) already returns a boolean. – Fabio Aug 30 '19 at 12:35
@Fabio Thanks buddy removed them to assign the Boolean value via the return type. – Magic Mick Sep 03 '19 at 04:10

score 1 · Answer 7 · edited May 03 '11 at 08:42

1

This will give you accurate result :

if ((expiryDate.Date - DateTime.Now.Date).Days < 30)
    matchFound = true;

edited May 03 '11 at 08:42

JPBlanc

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answered May 03 '11 at 07:13

Jayant

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actually what happens hr is eg.expryDte is 28/4/2011 if U rite (expiryDate-DateTime.now) it will take the time as well (28/4/2011 12:00:00 AM - 26/4/2011 11:47:00 AM) & above code takes value as 28/4/2011 12:00:00 AM -26/4/2011 12:00:00 AM which ill give accurate difference. – Jayant May 03 '11 at 09:29

score 0 · Answer 8 · answered Aug 02 '12 at 17:18

0

// this isn't set up for good processing.  
//I don't know what data set has the expiration 
//dates of your accounts.  I assume a list.
// matchfound is a single variablethat returns true if any 1 record is expired.

bool matchFound = false;
            DateTime dateOfExpiration = DateTime.Today.AddDays(-30);
            List<DateTime> accountExpireDates = new List<DateTime>();
            foreach (DateTime date in accountExpireDates)
            {
                if (DateTime.Compare(dateOfExpiration, date) != -1)
                {
                    matchFound = true;
            }
            }

answered Aug 02 '12 at 17:18

Alex

1

1

Isn't that a bit complicated? – Max Sep 27 '12 at 12:28
Where is the mention of accountExpireDates in the question? You copy pasted a bad solution. matchFound almost sounds like you're mixing Pattern or RegEx. Btw, you need to break when a match is found or it continues to loop. Also what if it is -2? MSDN does not say the possible values are -1, 0 and 1. – Mukus Feb 11 '14 at 01:19

score 0 · Answer 9 · answered Feb 09 '09 at 14:39

0

No, the Compare function will return either 1, 0, or -1. 0 when the two values are equal, -1 and 1 mean less than and greater than, I believe in that order, but I often mix them up.

answered Feb 09 '09 at 14:39

Timothy Carter

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score 0 · Answer 10 · answered Feb 09 '09 at 14:40

No you are not using it correctly.

See here for details.

DateTime t1 = new DateTime(100);
DateTime t2 = new DateTime(20);

if (DateTime.Compare(t1, t2) >  0) Console.WriteLine("t1 > t2"); 
if (DateTime.Compare(t1, t2) == 0) Console.WriteLine("t1 == t2"); 
if (DateTime.Compare(t1, t2) <  0) Console.WriteLine("t1 < t2");

score 0 · Answer 11 · answered Feb 09 '09 at 14:41

0

What you want to do is subtract the two DateTimes (expiryDate and DateTime.Now). This will return an object of type TimeSpan. The TimeSpan has a property "Days". Compare that number to 30 for your answer.

answered Feb 09 '09 at 14:41

GWLlosa

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score 0 · Answer 12 · answered Feb 09 '09 at 14:41

0

No it's not correct, try this :

DateTime expiryDate = DateTime.Now.AddDays(-31);
if (DateTime.Compare(expiryDate, DateTime.Now.AddDays(-30)) < 1)
{
    matchFound = true;
}

answered Feb 09 '09 at 14:41

Canavar

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vlad · Answer 13 · 2019-10-01T14:21:32.310

0

You can try to do like this:

var daysPassed = (DateTime.UtcNow - expiryDate).Days;
if (daysPassed > 30)
{ 
    // ...
}

edited Oct 01 '19 at 14:21

answered Sep 30 '19 at 11:38

vlad

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Please try to be more descriptive in your explanation. – borchvm Sep 30 '19 at 11:59

score 0 · Answer 14 · answered Nov 14 '11 at 15:21

Actually none of these answers worked for me. I solved it by doing like this:

  if ((expireDate.Date - DateTime.Now).Days > -30)
  {
    matchFound = true;
  }

When i tried doing this:

matchFound = (expiryDate - DateTime.Now).Days < 30;

Today, 2011-11-14 and my expiryDate was 2011-10-17 i got that matchFound = -28. Instead of 28. So i inversed the last check.

score -1 · Answer 15 · answered Sep 07 '11 at 10:26

-1

Compare is unnecessary, Days / TotalDays are unnecessary.

All you need is

if (expireDate < DateTime.Now) {
    // has expired
} else {
    // not expired
}

note this will work if you decide to use minutes or months or even years as your expiry criteria.

answered Sep 07 '11 at 10:26

rob

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Not a great answer because now you are also factoring in hours, minutes and seconds. DateTime.Today would be more correct for the OPs situation. – JL. Nov 07 '11 at 13:59

DateTime.Compare how to check if a date is less than 30 days old?

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