question about formulas in mortgage/loan druid

[Josh Sled]

On Wed, Jun 29, 2005 at 04:54:56PM -0400, Alan Munter wrote:
| I was trying to set up a loan in the druid and I am a bit confused
| about what all of the arguments to the ipmt, ppmt, and pmt functions
| are.

The best place to understand these is from the source itself.

gentoo installs the file fin.scm, which contains the definitions of these
functions into /usr/share/gnucash/scm/fin.scm.  As well, these functions
were copied from gnumeric, so their documentation should help.

| However, those are the bank terms of the loan.  I would like to repay
| the loan faster, so I would like the pmt amount to be, for example,
| $450 per month instead of $400.  Can I just go back and edit the
| scheduled transaction and in the "Credit Formula" replace
| pmt(0.039/12:24:10000:0:0) with the number 450 and leave the two Debit
| formulas alone to let them calculate it correctly?

Unfortunately, no.  The loan druid cannot handle the case where the loan
is repayed outside the straightforward repayment schedule defined by
the {,i,p}pmt functions.  Specifically, it cannot determine the interest
due based on the value of an account at a particular point in time.
E.g., after the first $450 payment, it can't determine that the interest 
should be 3.9% / 12 periods * $9550.

...jsled

-- 
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