I'm doing a annunity calculation:
payment = 331880*( 0,002458333 /( 1-(1+0,002458333)^-84) )
This will return me the payment per. month of the loan (4.337,76), over a period of 84 months.
Now, what i would like to know is what the payment per. month will be after a deduction of 33% tax on the interest rate. In the previous example (4.337,76) the result will be 4.236,91.
Etc. Loan before tax:
Month Interest Payment Total
0 815,87 3.561,88 4.377,76
1 807,12 3.570,64 4.377,76
2 798,34 3.579,42 4.377,76
Loan after tax:
Month Interest Payment Total
0 546,63 3.561,88 4.108,52
1 540,77 3.570,64 4.111,41
2 534,89 3.579,42 4.114,30
As you can see, the deduction is made to the interest, which is deducted by the 33%. ( Month 1: (851,86*0.67) = 546,63
I'm certain that there is a fancy method of doing this in the annunity calculation, without having to calculate a full table, fetching every single interest and doing the calculation there. I JUST cant find it!
Ive tried to deduct the 33% tax on the initial nominal interest rate 0.02458 * 0.67. But the results are not satisfying.
The formula for the anunity-calculation is as follows: (Not enough rep to post image. Link is: https://upload.wikimedia.org/math/4/9/0/49004d321caf393384ee4f211622a12c.png )
Where
Y = The amount to pay pr. period
G = Total amount to loan
r = The interest rate in decimals
n = the amount of payments
Any help would be greatly appreciated.