17BII, 27S: doing TVM calculations inside solver equations

[Csaba Tizedes]

(05-01-2019 12:58 PM)Dave Britten Wrote:  I'll explain the specific problem in more detail, in case there's an easier way to do it that doesn't involve TVM.

I'm trying to make a solver formula that will calculate the amount of interest saved over the remaining life of a loan if I were to make an extra principal pay-down of a given size.

2. Subtract the extra principal payment from PV, and update PV.
3. Recalculate N to determine the new number of payments remaining to pay off the reduced principal.

Two notes to this:

1. This is total same what I programmed approx 2 months before on my 12C, except your point 3.), because:
2. In Hungary if you change the number of periods (which is written in your contract) you must to make a new contract (contract modification) - but you have a possibility to pay principal as prepayment. This will reduce your PV but not your N. Of course, your PMT also reduced.
   

Therefore in real life the good solution to calculate the required periods to reduce the PV below your monthly payment, and then you can pay the whole PV.
So, you need to make a table: 1st Coloumn: Your prepayment (eg. in every 6 periods or every 12 periods), 2nd Coloumn: The required N for reducing PV<=PMT

With this table you can easily decide what is the preferred prepayment or N for you.

Csaba