Strangeness in Mortgage/Loan Repayment Druid
jsled at asynchronous.org
Tue Jul 1 19:43:40 CDT 2003
On Tue, Jul 01, 2003 at 07:59:40PM -0400, Daniel Hannum wrote:
| I have a number of questions about the mortgage/loan repayment druid.
| BTW, I'm on 1.8.1 (redhat 9). So I this has been fixed, please let me
| know. I'm not prepared to grapple with upgrading (yet)... it was easier
| under Debian......
I don't believe the Mortgage/Loan druid has seen any changes since 1.8.0.
| Now, when I put the principal, rate and term into Gnucash's druid, it
| comes up with 374.13, but that's not good, because that's not what I'm
| actually going to pay.
4 whole cents off? Good enough for government work... ;)
If it's a constant 0.04, you could modify the formulae to add/subtract that
out, but that's a nasty hack. OTOH, it might solve your immediate problem,
though I imagine that the rest of the calculations would be off, as well. :(
I had expected that the calculation would vary from most people's actual
payments for various reasons ... this is a good example of this. Sorry.
| 1. How do I force a particular loan payment? On the page of the Druid
| where you specify the 'Amount' and the accounts where the principal and
| interest will be, I tried replacing the "pmt()" expression with $374.09,
| but it seemed to ignore me; the next page still had 60 payments of $374.13
Hmm... that should actually work, IIRC.
In playing with it, it does look like any changes made to the Payment
field are ignored, which is quite unfortunate. Filing a bug at
bugzilla.gnome.org is appreciated.
| 2. What does "pmt( 0.07900 / 12 : 60 : 18495.00 : 0 : 0 )" mean?
| Obviously, it's rate, term, principal, but what are the last 2 zeroes?
| Perhaps I shouldn't care. Or perhaps it could help to know.
This one can be answered by looking in src/scm/fin.scm [I forget where
it's copied on install, but `locate fin.scm` should find it] -- the last
two terms are the "future value" and "type", as defined by the Gnumeric
1.0.8 functions of the same name. Future value could be non-zero, but
I made the simplifying that it is.
I was hoping to have a more name=value function syntax in the future, but
time's a bitch.
| 3. If I were to start paying the loan off faster, with irregular
| amounts, I would have to put these transactions in by hand. Does it seem
| correct to take the balance after the previous payment, multiply it by
| 7.9%/12 and use that as the interest portion? I would think that would
| be right, but when I try that with the current balance, it doesn't come
| up the same as what the scheduled transaction generator is producing...
| so you guys must have a different algorithm.
Yes ... there's an existing bug [and some design-time requests which were
not incorporated] that any future transactions should be based on the
present value of the account at the time of payment... this would be a
nice expansion of the feature. :(
| Any help would be appreciated.
I fear that wasn't a lot of help, unfortunately, but hopefully it's
more clear. My time to enhance this [or any] part of the codebase is
non-existant at present, a situation I don't think will be resolved for
some number of months. Hopefully someone will step up to this.
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