SurreyWebDesigner
asked on
How do I convert this Excel formula into something I can use in PHP?
Hi,
I'm creating a mortgage calculator for a client and he's given me a spreadsheet with the formulas in. The problem is that the formula uses an Excel function called PMT. This is the formula:
= - PMT ( R/12 , T*12 , A , 0 , 0 )
where R is the interest Rate (e.g. 10%)
T is the Term of the loan (e.g. 30 years)
and A is the Amount of the loan (e.g. 100,000)
The question is, how do I convert this into something I can put in PHP code to do the work on a webpage instead of in a spreadsheet??
Thanks
SWD
Please note: I had already asked this question but incorrectly put it in the Excel forum - it has since been moved to the PHP forum but I was concerned that it was getting the visibility that it would if I'd submitted it here straight away. I have requested that the existing question be removed. (https://www.experts-exchange.com/questions/21785434/Converting-Excel's-PMT-function-to-use-in-PHP.html)
I'm creating a mortgage calculator for a client and he's given me a spreadsheet with the formulas in. The problem is that the formula uses an Excel function called PMT. This is the formula:
= - PMT ( R/12 , T*12 , A , 0 , 0 )
where R is the interest Rate (e.g. 10%)
T is the Term of the loan (e.g. 30 years)
and A is the Amount of the loan (e.g. 100,000)
The question is, how do I convert this into something I can put in PHP code to do the work on a webpage instead of in a spreadsheet??
Thanks
SWD
Please note: I had already asked this question but incorrectly put it in the Excel forum - it has since been moved to the PHP forum but I was concerned that it was getting the visibility that it would if I'd submitted it here straight away. I have requested that the existing question be removed. (https://www.experts-exchange.com/questions/21785434/Converting-Excel's-PMT-function-to-use-in-PHP.html)
ASKER
Hi siliconbrit - thanks for posting ...
This is what I now have:
$varA = $_REQUEST['Amount'];
$varR = $_REQUEST['Rate'];
$varT = $_REQUEST['Term'];
$x = 1 / (1 + ( $varR / 12 ) );
$RepaymentAmount = round(( ( 1 - $x ) * $varA) / ($x * (1 - pow( $x, $varT ) ) ),2);
But when I display $RepaymentAmount it comes out at £46042.59 (when I use 85,000 as the amount, 6.5 as the rate and 25 as the term).
I actually use another formula to calculate the repayments on an interest only mortgage:
$InterestOnlyAmount = round((($varA * $varR / 100) / 12), 2);
Given the same values (85,000 - 6.5 and 25) it comes out to £460.42 per month (1/100th of the amount given for $RepaymentAmount).
From what I'm told, using the PMT function in Excel to calculate the repayment amount would give a figure of £573.93 per month - so i'm a bit out at the moment.
Thanks for your help.
SWD
This is what I now have:
$varA = $_REQUEST['Amount'];
$varR = $_REQUEST['Rate'];
$varT = $_REQUEST['Term'];
$x = 1 / (1 + ( $varR / 12 ) );
$RepaymentAmount = round(( ( 1 - $x ) * $varA) / ($x * (1 - pow( $x, $varT ) ) ),2);
But when I display $RepaymentAmount it comes out at £46042.59 (when I use 85,000 as the amount, 6.5 as the rate and 25 as the term).
I actually use another formula to calculate the repayments on an interest only mortgage:
$InterestOnlyAmount = round((($varA * $varR / 100) / 12), 2);
Given the same values (85,000 - 6.5 and 25) it comes out to £460.42 per month (1/100th of the amount given for $RepaymentAmount).
From what I'm told, using the PMT function in Excel to calculate the repayment amount would give a figure of £573.93 per month - so i'm a bit out at the moment.
Thanks for your help.
SWD
ASKER CERTIFIED SOLUTION
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...which prints out "573.9260871455", which is rounded to 573.93$.
ASKER
Spot on!!! Thanks very much aib_42!!!
Cheers
SWD
Cheers
SWD
aib_42: this is perfect, what if there is a balance at the end of the period, how would it work. very similar to the one on excel
or with fv, future value
This will probably give you what you want, but slightly different from the Excel equivalent, so you'll have to play with it a little:
T = Term of the loan in years
R = Annual interest rate expressed as a Decimal (10% = 0.1)
A = Amount of the loan.
function PMT ($T, $R, $A ) {
$x = 1 / (1 + ( $R / 12 ) );
return ( ( 1 - $x ) * $A) / ($x * (1 - pow( $x, $T ) ) );
}
Note that I haven't tested this against the Excel PMT, I've just re-written an old C++ function I have to achive the same in PHP.