Add six months to a start date

[sandy]

Hi,
Using Java script I am trying to create code where when you place in
the start date it automatically calculates 6 months for the
experations date. For example when I place 01/01/04 as the issue date
the experation date should automaically generate as 06/01/04. I would
appreciate it if anyone could help me.

Thank you
Sandy

[Dennis M. Marks]

I have read the following message from sa**********@ya hoo.com (sandy)
and have decided to lend my vast knowledge.

The writer said:

Hi,
Using Java script I am trying to create code where when you place in
the start date it automatically calculates 6 months for the
experations date. For example when I place 01/01/04 as the issue date
the experation date should automaically generate as 06/01/04. I would
appreciate it if anyone could help me.

Thank you
Sandy

and my reply is:
The following must be considered before an answer can be given. What if
the date is the 31st and there is no 31st six months later?

What is six months after 03/31/04?

BTW: Six months after 01/01/04 is 07/01/04 not 06/01/04.

--
Dennis M. Marks
http://www.dcs-chico.com/~denmarks/
Replace domain.invalid with dcsi.net
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[Mike]

Here is a simple script that may get you started.

var date = new Date();
var date6MonthsFrom Now = new Date(date.getTi me() + (182*24*60*60*1 000));

the formula is simply [current time in mils + (#days in 6 months * #hrs in
day * #mins in hrs * #sec in min * #mils in sec)]

Regards
Mike

[Randy Webb]

Mike <mi************ *****@synovic.c om> wrote:

Here is a simple script that may get you started.

var date = new Date();
var date6MonthsFrom Now = new Date(date.getTi me() + (182*24*60*60*1 000));

the formula is simply [current time in mils + (#days in 6 months * #hrs in
day * #mins in hrs * #sec in min * #mils in sec)]

How many days are in 6 months depends directly on what 6 month span you
cover.

Of the 12 6 month spans that can be covered, only 2 have 182 days:

Jan-Jun 181 days
Feb-July 181 days
Mar-Aug 184 days
Apr-Sep 183 days
May-Oct 184 days
Jun-Nov 183 days
July-Dec 184 days
Aug-Jan 184 days
Sep-Feb 181 days
Oct-Mar 182 days
Nov-Apr 181 days
Dec-May 182 days

Means that your script is only right 1/6 (or ~17% of the time), not what
I would consider very efficient.

And that does not take into account leap day every 4 years, which is a
problem of its own and introduces 6 more possibilities:

Feb-July 182 days
Mar-Aug 185 days
Apr-Sep 184 days
May-Oct 185 days
Jun-Nov 184 days
July-Dec 185 days
Aug-Jan 185 days

but your correctness ratio is still 1/6.

--
Randy

[rf]

"Dennis M. Marks" <de******@domai n.invalid> wrote in message
news:1201200415 43585567%de**** **@domain.inval id...

I have read the following message from sa**********@ya hoo.com (sandy)
and have decided to lend my vast knowledge.

BTW: Six months after 01/01/04 is 07/01/04 not 06/01/04.

Over here six months after 01/01/04 is 01/07/04 :-)

Cheers
Richard.

[Willie Lau]

Try this:

Date.prototype. addMonths = function(n)
{
this.setMonth(t his.getMonth()+ n);
return this;
}

var d = new Date().addMonth s(6);

Regards,
Willie

[Willie Lau]

Try this:

Date.prototype. addMonths = function(n)
{
this.setMonth(t his.getMonth()+ n);
return this;
}

var d = new Date().addMonth s(6);

Regards,
Willie

[Harag]

not tested... but I dont think that will work

say the date is 31st March 2004

if you add 6 months to that you would end up with 31st September
2004... Which is a problem because there isn't 31 days in September.

The best way is to always calculate in days...

6 months = 26 weeks (52/2)

26 weeks *7 = 182

So your best always adding 182 to the date.

HTH

Al.

On 12 Jan 2004 23:22:38 -0800, wi****@brainjac ked.com (Willie Lau)
wrote:

Try this:

Date.prototype .addMonths = function(n)
{
this.setMonth(t his.getMonth()+ n);
return this;
}

var d = new Date().addMonth s(6);

Regards,
Willie

[Harag]

I'd have to disagree with this and agree with mikes

they are 52 weeks in a year. or 12 months.

so 6 months is 26 weeks and a quarter is 13 weeks

they are 7 days a week

so 6 months = 26 * 7 = 182 days
or a quarter = 13 * 7 = 91 days

If you want to add just a month then that is the difficult one to do
as there isn't any set number of week so to work that out we go.

13 weeks / 3 = 4.3333333 weeks per month.
4.3333333 * 7 = 30.3333333 DAYS per month

so if you want to add one month you need to add the following number
of milliseconds to the date:

1000 * 60 * 60 * 24 * 30.33333333 = 2620800000

var date1MonthsFrom Now = new Date(date.getTi me() +
parseInt(30.333 3333*24*60*60*1 000));

var date6MonthsFrom Now = new Date(date.getTi me() + (182*24*60*60*1 000));

so by adding 182 days, like mike has done here is the correct way to
add "6 months"

Al.
On Mon, 12 Jan 2004 21:33:07 -0500, Randy Webb
<hi************ @aol.com> wrote:
Mike <mi************ *****@synovic.c om> wrote:

Here is a simple script that may get you started.

var date = new Date();
var date6MonthsFrom Now = new Date(date.getTi me() + (182*24*60*60*1 000));

the formula is simply [current time in mils + (#days in 6 months * #hrs in
day * #mins in hrs * #sec in min * #mils in sec)]

How many days are in 6 months depends directly on what 6 month span you
cover.

Of the 12 6 month spans that can be covered, only 2 have 182 days:

Jan-Jun 181 days
Feb-July 181 days
Mar-Aug 184 days
Apr-Sep 183 days
May-Oct 184 days
Jun-Nov 183 days
July-Dec 184 days
Aug-Jan 184 days
Sep-Feb 181 days
Oct-Mar 182 days
Nov-Apr 181 days
Dec-May 182 days

Means that your script is only right 1/6 (or ~17% of the time), not what
I would consider very efficient.

And that does not take into account leap day every 4 years, which is a
problem of its own and introduces 6 more possibilities:

Feb-July 182 days
Mar-Aug 185 days
Apr-Sep 184 days
May-Oct 185 days
Jun-Nov 184 days
July-Dec 185 days
Aug-Jan 185 days

but your correctness ratio is still 1/6.

[Randy Webb]

Harag wrote:

I'd have to disagree with this and agree with mikes

they are 52 weeks in a year. or 12 months.

so 6 months is 26 weeks and a quarter is 13 weeks
That depends directly on your definition of a month.

they are 7 days a week

so 6 months = 26 * 7 = 182 days
or a quarter = 13 * 7 = 91 days

If you want to add just a month then that is the difficult one to do
as there isn't any set number of week so to work that out we go.

13 weeks / 3 = 4.3333333 weeks per month.
4.3333333 * 7 = 30.3333333 DAYS per month

so if you want to add one month you need to add the following number
of milliseconds to the date:

1000 * 60 * 60 * 24 * 30.33333333 = 2620800000

var date1MonthsFrom Now = new Date(date.getTi me() +
parseInt(30.333 3333*24*60*60*1 000));
And you will still be wrong. There are not 30.3333333 days in a month,
any month. So now you are wrong 6 out of 6 instead of 5 out of 6 times.

var date6MonthsFrom Now = new Date(date.getTi me() + (182*24*60*60*1 000));

so by adding 182 days, like mike has done here is the correct way to
add "6 months"

No its not.

Please read the FAQ.

--
Randy