Savings made by making a fix extra payment every moth to a loan

[Guilder]

I have the fallowing loan:


Principal: $72 222.22
Rate: 10.5%
Year: 15
Payments are made monthly.
The first payment will be made on January 2016

For 15 cells that correspond to each year of the loan; I need the formula that will determine how much interest will be save if a $10 fix extra monthly payment was to be made; starting the responding year of the cell, until the loan is paid off.
So in one cell the formula will determine how much interest will be save if the $10 extra payments had started on Jan 2016
In another the formula will determine how much interest will be save if the $10 extra payments had started on Jan 2017 and no extra payments was made during the first year of the loan.
In another the formula will determine how much interest will be save if the $10 extra payments had started on Jan 2018 and no extra payments was made during the two years of the loan.
And so on…
I think that “FV” may help, but I was not able to get it to work.

 

[revcanon]

You might try looking at this site to see if an existing spreadsheet would give you the answer you are looking for:

Extra Payment Mortgage Calculator for Excel

 

[Guilder]

Thank you Revcanon, that site di not really answer my question.

 

[Guilder]

I think the problem has been solve.
I have been dividing the interest rate by 12, and not the way it is supposed to be.

If I calculate supposing that I start making the $10 extra payment from the very first moth I do:


=FV((1+Interest_Rate)^(1/12)-1,J7+1,-10,-10)

In J7 I have:
=ROUNDUP(NPER((1+Interest_Rate)^(1/12)-1,-(J8)+10),72222.22),0)

In J8 I have:
=-PMT((1+10.5%)^(1/12)-1,15*12,72222.22)



That give me $4,022.76 and it should give me $4,022.16, so there is a $0.60 difference that may very well be a "Rounding error".

I am sorry, but I no longer fallow the logic of the formula.
Am I calculating something wrong, or is that how it is supposed to be?