Fwd: Adding to a date

Sorry, forgot to include the group in my reply...

---------- Forwarded message ----------
From: Harold A. Giménez Ch. <harold(dot)gimenez(at)gmail(dot)com>
Date: Mon, Jun 30, 2008 at 5:51 PM
Subject: Re: [NOVICE] Adding to a date
To: Mike Ellsworth <younicycle(at)gmail(dot)com>

Intervals might help...for example:

timestamp '2001-09-28 01:00' + interval '23 hours' = timestamp
'2001-09-29 00:00:00'

Taken from here:
http://www.postgresql.org/docs/8.3/interactive/functions-datetime.html

On Mon, Jun 30, 2008 at 5:44 PM, Mike Ellsworth <younicycle(at)gmail(dot)com> wrote:
>
> I was beginning to create some financial functions for calculating
> Future Values, PV's, etc -for basic retirement planning.
> example:
>
> CREATE OR REPLACE FUNCTION lotsa.FVPMT(payment double precision,
> interestRate double precision, periods double precision)
> RETURNS double precision AS
> $BODY$
> BEGIN
> return payment*(pow(1+interestRate, periods)-1)/interestRate;
> END;
> $BODY$
> LANGUAGE 'plpgsql' VOLATILE
>
> periods seems to be a problem. Usually, I'd be getting birth_date
> from a file, but I'm not finding a way to
> add 65 years - or 67 or whatever, to get the period between now (or an
> assumed date) and retirement.
>
> I'm hoping there is a way to:
> 1) Date of birth + xx years - with a result of date (Result 1)
> 2) Subtract now or an assumed date from Result 1 to get Result 2
> 3) Divide by ~ 365.25 for years, which would be 'periods' in the function.
>
> I've gotten around it, but it sure seems pretty messy:
> Greatest(FVPMT(test_fv.pmt, test_fv.i_rate,
> (23741.25-(test_fv.start_date-test_fv.dob))/365.25),0)
>
> where the 23741.25 is 65* 365.25.
>
> Any help would be appreciated. I've read all of what would seem to be
> appropriate.
> Doesn't mean I understood it, but I read it.
>
> I'm not concerned about being off by a day or 2.
> Small potatoes compared to the variations rate of return will undergo.
>
> Thanks
>
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