# Calculate last day of month **URL:** \ **Category:** Ruby\ **Created:** [September 21, 2006, 9:00pm UTC](https://www.ruby-forum.com/t/calculate-last-day-of-month/69561 "2006-09-21T21:00:04Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![siguva](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/c5a1d2/32.png) [@siguva](https://www.ruby-forum.com/u/siguva)\ **Post date:** [September 21, 2006, 9:00pm UTC](https://www.ruby-forum.com/t/calculate-last-day-of-month/69561/1 "2006-09-21T21:00:04Z")
This is probably an easy one for somebody, but I couldn’t figure it out using the Date class in the documentation. require ‘date’ d = Date.new(2006, 9,16) How do I return the date for the last day of this month (September in this example)? Thank you for your help! -Hunter ---
**Author:** ![siguva](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/c5a1d2/32.png) [@siguva](https://www.ruby-forum.com/u/siguva)\ **Post date:** [September 21, 2006, 9:11pm UTC](https://www.ruby-forum.com/t/calculate-last-day-of-month/69561/2 "2006-09-21T21:11:11Z")
Hunter W. wrote: > This is probably an easy one for somebody, but I couldn’t figure it out > using the Date class in the documentation. > > How do I return the date for the last day of this month (September in > this example)? Easy: Construct a date for the first day of the following month, then subtract one day and read the resulting components. Hard: construct a date for the first day of the target month, then add days unitil the month number changes. Then go back one. I think I know which option you’ll choose. 🙂 ---
**Author:** ![siguva](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/c5a1d2/32.png) [@siguva](https://www.ruby-forum.com/u/siguva)\ **Post date:** [September 21, 2006, 9:49pm UTC](https://www.ruby-forum.com/t/calculate-last-day-of-month/69561/3 "2006-09-21T21:49:57Z")
Very cool! That worked! Thank you! -Hunter ---
**Author:** ![siguva](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/c5a1d2/32.png) [@siguva](https://www.ruby-forum.com/u/siguva)\ **Post date:** [September 21, 2006, 9:37pm UTC](https://www.ruby-forum.com/t/calculate-last-day-of-month/69561/4 "2006-09-21T21:37:13Z")
On Fri, 22 Sep 2006, Paul L. wrote: > Hard: construct a date for the first day of the target month, then add days > unitil the month number changes. Then go back one. > > I think I know which option you’ll choose. 🙂 except you have to handle december specially - else you’ll end up with the with the wrong year. easiest is probably: harp:~ \> cat a.rb require ‘date’ class Date def self.last\_day\_of\_the\_month yyyy, mm d = new yyyy, mm d += 42 # warp into the next month new(d.year, d.month) - 1 # back off one day from first of that month end end puts Date.last\_day\_of\_the\_month(2006, 9) puts Date.last\_day\_of\_the\_month(2006, 12) puts Date.last\_day\_of\_the\_month(2007, 2) harp:~ \> ruby a.rb 2006-09-30 2006-12-31 2007-02-28 -a ---
**Author:** ![siguva](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/c5a1d2/32.png) [@siguva](https://www.ruby-forum.com/u/siguva)\ **Post date:** [September 21, 2006, 10:15pm UTC](https://www.ruby-forum.com/t/calculate-last-day-of-month/69561/5 "2006-09-21T22:15:18Z")
> ``` > d += 42 # warp into the next month > > ``` You need to add a month, not a fixed number of days, since you can’t predict how many days are in the next month: irb(main):033:0\> d = Date.new 2006, 1, 31 =\> #\ irb(main):034:0\> (d \>\> 1).to\_s =\> “2006-02-28” irb(main):039:0\> d = Date.new 1996, 1, 31 =\> #\ irb(main):040:0\> (d \>\> 1).to\_s =\> “1996-02-29” - James M. ---
**Author:** ![siguva](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/c5a1d2/32.png) [@siguva](https://www.ruby-forum.com/u/siguva)\ **Post date:** [September 21, 2006, 10:41pm UTC](https://www.ruby-forum.com/t/calculate-last-day-of-month/69561/6 "2006-09-21T22:41:25Z")
> How do I return the date for the last day of this month (September in > this example)? Looking for an alternate way: could this be a step in the right direction? (See [http://chronic.rubyforge.org/](http://chronic.rubyforge.org/)) irb(main):001:0\> require ‘chronic’ irb(main):011:0\> Chronic.parse(‘last day of this month’) =\> nil Well… this was close. 🙂 ---
**Author:** ![siguva](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/c5a1d2/32.png) [@siguva](https://www.ruby-forum.com/u/siguva)\ **Post date:** [September 21, 2006, 10:57pm UTC](https://www.ruby-forum.com/t/calculate-last-day-of-month/69561/7 "2006-09-21T22:57:27Z")
On 21/09/06, Hunter W. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > How do I return the date for the last day of this month (September in > this example)? Date.new((Date.today\>\>1).year,(Date.today\>\>1).month,1)-1) -Thomas ---
**Author:** ![siguva](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/c5a1d2/32.png) [@siguva](https://www.ruby-forum.com/u/siguva)\ **Post date:** [September 21, 2006, 10:21pm UTC](https://www.ruby-forum.com/t/calculate-last-day-of-month/69561/8 "2006-09-21T22:21:20Z")
On 9/21/06, James M. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > irb(main):039:0\> d = Date.new 1996, 1, 31 > =\> #\ > irb(main):040:0\> (d \>\> 1).to\_s > =\> “1996-02-29” > > - James M. Yeah that was my first thought too, but notice he is constructing a new date at the beginning of the month. I am guessing he picked 42, over 32 as it is just much better number. pth ---
**Author:** ![siguva](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/c5a1d2/32.png) [@siguva](https://www.ruby-forum.com/u/siguva)\ **Post date:** [September 22, 2006, 12:01am UTC](https://www.ruby-forum.com/t/calculate-last-day-of-month/69561/9 "2006-09-22T00:01:34Z")
removed\_email\_address@domain.invalid wrote: > On Fri, 22 Sep 2006, Patrick H. wrote: > > > Yeah that was my first thought too, but notice he is constructing a > > new date at the beginning of the month. I am guessing he picked 42, > > over 32 as it is just much better number. > > exactly 😉 > > the point is that it always lands into the next month. Or the month after that - depending on where you start. 🙂 ``` robert ``` ---
**Author:** ![siguva](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/c5a1d2/32.png) [@siguva](https://www.ruby-forum.com/u/siguva)\ **Post date:** [September 21, 2006, 11:05pm UTC](https://www.ruby-forum.com/t/calculate-last-day-of-month/69561/10 "2006-09-21T23:05:29Z")
On Fri, 22 Sep 2006, Patrick H. wrote: > Yeah that was my first thought too, but notice he is constructing a > new date at the beginning of the month. I am guessing he picked 42, > over 32 as it is just much better number. exactly 😉 the point is that it always lands into the next month. -a ---
**Author:** ![siguva](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/c5a1d2/32.png) [@siguva](https://www.ruby-forum.com/u/siguva)\ **Post date:** [September 22, 2006, 12:11am UTC](https://www.ruby-forum.com/t/calculate-last-day-of-month/69561/11 "2006-09-22T00:11:34Z")
On Fri, 22 Sep 2006, Robert K. wrote: > Or the month after that - depending on where you start. 🙂 sure - but it always starts on the first day of the month: require ‘date’ class Date def self.last\_day\_of\_the\_month yyyy, mm d = new yyyy, mm # no day means the first one d += 42 # always the next month new(d.year, d.month) - 1 end end puts Date.last\_day\_of\_the\_month(2006, 9) puts Date.last\_day\_of\_the\_month(2006, 12) puts Date.last\_day\_of\_the\_month(2007, 2) cheers. -a ---
**Author:** ![siguva](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/c5a1d2/32.png) [@siguva](https://www.ruby-forum.com/u/siguva)\ **Post date:** [September 22, 2006, 9:16am UTC](https://www.ruby-forum.com/t/calculate-last-day-of-month/69561/12 "2006-09-22T09:16:35Z")
removed\_email\_address@domain.invalid wrote: > > > the point is that it always lands into the next month. > > > > Or the month after that - depending on where you start. 🙂 > > sure - but it always starts on the first day of the month: Yes, of course. I didn’t want to insunuate you code would not do what you claimed it to do. It was merely a silly remark, probably stirred up by this strange number that I haven’t seen in a while. I am sorry. Kind regards ``` robert ``` ---
**Author:** ![siguva](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/c5a1d2/32.png) [@siguva](https://www.ruby-forum.com/u/siguva)\ **Post date:** [September 22, 2006, 5:11pm UTC](https://www.ruby-forum.com/t/calculate-last-day-of-month/69561/13 "2006-09-22T17:11:39Z")
I’ve had this problem often enough to make a gem of my solution: require ‘expanded\_date’ d = Date.new =\> 2006-09-22 d.end\_of\_month =\> 2006-09-30 d.end\_of\_next\_month =\> 2006-10-31 The gems is in production use and will continue to be maintained. Any feedback would be welcome. Rdoc: [http://backofficegems.rubyforge.org/expanded\_date/doc/](http://backofficegems.rubyforge.org/expanded_date/doc/) ---
**Author:** ![siguva](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/c5a1d2/32.png) [@siguva](https://www.ruby-forum.com/u/siguva)\ **Post date:** [September 22, 2006, 9:06pm UTC](https://www.ruby-forum.com/t/calculate-last-day-of-month/69561/14 "2006-09-22T21:06:02Z")
Hunter W. wrote: > This is probably an easy one for somebody, but I couldn’t figure it out > using the Date class in the documentation. > > require ‘date’ > > d = Date.new(2006, 9,16) > > How do I return the date for the last day of this month (September in > this example)? > > Thank you for your help! > > -Hunter Date.new(2006, 9,-1) -1 means count backwards in this context. more info at [http://www.ruby-doc.org/core/classes/Date.html#M001193](http://www.ruby-doc.org/core/classes/Date.html#M001193) ---
**Author:** ![siguva](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/c5a1d2/32.png) [@siguva](https://www.ruby-forum.com/u/siguva)\ **Post date:** [July 16, 2008, 2:38pm UTC](https://www.ruby-forum.com/t/calculate-last-day-of-month/69561/15 "2008-07-16T14:38:24Z")
On Wed, Jul 16, 2008 at 11:41:32AM +0900, Platoon Tb wrote: > class Date > def self.last\_day\_of\_the\_month(yyyy, mm) > new(yyyy, mm).next\_month - 1 > end > end It’s easier than that. class Date def self.last\_day\_of\_the\_month(yyyy, mm) new(yyyy, mm, -1) end end –Greg ---
**Author:** ![siguva](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/c5a1d2/32.png) [@siguva](https://www.ruby-forum.com/u/siguva)\ **Post date:** [July 16, 2008, 4:45am UTC](https://www.ruby-forum.com/t/calculate-last-day-of-month/69561/16 "2008-07-16T04:45:48Z")
class Date def self.last\_day\_of\_the\_month(yyyy, mm) new(yyyy, mm).next\_month - 1 end end ---
**Author:** ![siguva](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/c5a1d2/32.png) [@siguva](https://www.ruby-forum.com/u/siguva)\ **Post date:** [July 16, 2008, 3:50pm UTC](https://www.ruby-forum.com/t/calculate-last-day-of-month/69561/17 "2008-07-16T15:50:04Z")
Gregory S. wrote: > It’s easier than that. > > class Date > def self.last\_day\_of\_the\_month(yyyy, mm) > new(yyyy, mm, -1) > end > end Why override Date at all when we’ve got ActiveSupport::CoreExtensions:📅:Calculations and can just use ‘end\_of\_month’? ---
**Author:** ![siguva](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/c5a1d2/32.png) [@siguva](https://www.ruby-forum.com/u/siguva)\ **Post date:** [July 16, 2008, 3:11pm UTC](https://www.ruby-forum.com/t/calculate-last-day-of-month/69561/18 "2008-07-16T15:11:21Z")
Ok, I know that I am going to be smacked for this, but we DO know how many days are in each month. Why not just have one for february with considerations for leap year, and lists for those with 30 and 31 days, or possibly 30 days and everything else has 31. It is nothing more than a lookup. Is that too easy or too non Ruby-ish? ---
**Author:** ![siguva](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/c5a1d2/32.png) [@siguva](https://www.ruby-forum.com/u/siguva)\ **Post date:** [July 16, 2008, 4:22pm UTC](https://www.ruby-forum.com/t/calculate-last-day-of-month/69561/19 "2008-07-16T16:22:30Z")
On Wed, Jul 16, 2008 at 10:44:35PM +0900, Bill W. wrote: > Why override Date at all when we’ve got > ActiveSupport::CoreExtensions:📅:Calculations and can just use > ‘end\_of\_month’? Because this is the ruby list, not the rubyonrails list. –Greg ---
**Author:** ![siguva](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/c5a1d2/32.png) [@siguva](https://www.ruby-forum.com/u/siguva)\ **Post date:** [July 16, 2008, 7:00pm UTC](https://www.ruby-forum.com/t/calculate-last-day-of-month/69561/20 "2008-07-16T19:00:39Z")
Gregory S. wrote: > On Wed, Jul 16, 2008 at 10:44:35PM +0900, Bill W. wrote: > > > Why override Date at all when we’ve got > > ActiveSupport::CoreExtensions:📅:Calculations and can just use > > ‘end\_of\_month’? > > Because this is the ruby list, not the rubyonrails list. > > –Greg Oops 😉 Should have checked the header. My bad. Best regards, Bill