php - Annunity calculation before and after tax -
i'm doing annunity calculation through script:
$calculation= ( 400000 * 0.02458/( 1- pow( 1+(0.02458) , -84) ) ) ; return round($calculation,2);
this return me payment per. month of loan (4.337,76), on period of 84 months.
now, know payment per. month after deduction of 33% tax on interest rate. in previous example (4.337,76)
result 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 can see, deduction made interest, deducted 33%. ( month 1: (851,86*0.67) = 546,63
i'm there fancy method of doing in annunity calculation, without having calculate full table, fetching every single interest , doing calculation there. cant find it!
looking forward great answers
if i'm understanding correctly want correlate taxes in interest rate right? have say:
r-real = r-nom * (1-t)
where r-real
interest after taxes, r-nom
before taxes , t = taxes
.
i've pasted quick excel example image.
http://i.stack.imgur.com/wqyxe.png
i hope makes sense.
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