(17B/19B) GPM: initial payment

[Werner]

(06-17-2024 08:32 PM)Gil Wrote:  I find, Werner, your formulation —certainly correct — somewhat confusing:

N: 360 - number of payment periods (30 years, 12 payments per year)
PV: 60000 - present value
I%: 1 - periodic rate (annual rate I%YR=12 divided by NP=12)
NP: 12 - number of payment periods per growth period (a year)
G%: 7.5 - growth rate per growth period
NG: 5 - number of growth periods

We might think wrongly NG=5 months, instead of 5 years, with frequency change in a year = 1.

I would've thought you'd find the calculation procedure confusing ;-)
But you are right: the word 'periods' should not be used for payments. I'll change it in the post.
So, it's 'total number of payments', 'number of payments per growth period' etc. I just did not want to be tied down to payments that grow each year only.

Quote:I suppose your result -474.8251297 is due to rounding, as the correct one should be -474.8251298 (-474.825129768).

The 12C only carries 10 digits. I'd say that 1 ULP off is not bad for a 40-year old calculator? It is a rather involved calculation, after all.

Cheers, Werner