dataxspy Posted July 26, 2020 Share Posted July 26, 2020 (edited) I tried using a for loop but I'm trying to think of a way to calculate interest for a number of years but after I have the amount of interest for one year I'm unsure of how to add the interest to the principle then calculate it again for the next year, to hold that number like $Principle + $Interest = $NewPrinciple then $NewPrinciple + $Interest for multiple years. <?php if (isset($_POST['submit'])) { $InvestmentFrequency = $_POST['InvestmentFrequency']; $CompoundFrequency = $_POST['CompoundFrequency']; $InitialInvestment = preg_replace("/[^0-9]/", '', $_POST['InitialInvestment']); $Contributions = preg_replace("/[^0-9]/", '', $_POST['Contributions']); $InvestmentLength = preg_replace("/[^0-9]/", '', $_POST['InvestmentLength']); $InterestRate = $_POST['InterestRate']; if ($InvestmentFrequency == "Weekly") { $InvestmentFrequency = "52"; } elseif ($InvestmentFrequency == "Monthly") { $InvestmentFrequency = "12"; } else { $InvestmentFrequency = "1"; } if ($CompoundFrequency == "Annually") { $CompoundFrequency = "1"; } elseif ($CompoundFrequency == "Semiannually") { $CompoundFrequency = "2"; } elseif ($CompoundFrequency == "Monthly") { $CompoundFrequency = "12"; } elseif ($CompoundFrequency == "Weekly") { $CompoundFrequency = "52"; } else { $CompoundFrequency = "365"; } if ($CompoundFrequency == "1") { $AdditionalInvestments = $Contributions * $InvestmentFrequency; $Principle = $InitialInvestment + $AdditionalInvestments; $Interest = $Principle * $InterestRate; $NewPrinciple = $Principle + $Interest; for ($x = 0; $x <= $InvestmentLength; $x++){ echo "$x - $NewPrinciple</br>"; } } } This is the output I get the principle and interest added together for the number of years I entered. Edited July 26, 2020 by dataxspy Quote Link to comment https://forums.phpfreaks.com/topic/311228-calculating-compound-interest/ Share on other sites More sharing options...
requinix Posted July 27, 2020 Share Posted July 27, 2020 What if I told you that you don't need a loop? 1 Quote Link to comment https://forums.phpfreaks.com/topic/311228-calculating-compound-interest/#findComment-1580128 Share on other sites More sharing options...
gw1500se Posted July 27, 2020 Share Posted July 27, 2020 (edited) Adapt the standard compound interest formula: A=P(1+r/n)^(nt) Where: A= amount P=principle r= interest rate n= number of compoundings per year t= number of time periods For continuous compounding use: A=Pe^(rt) Where: t=time in years (can be a fraction) e= mathematical constant (2.71828) Edited July 27, 2020 by gw1500se Quote Link to comment https://forums.phpfreaks.com/topic/311228-calculating-compound-interest/#findComment-1580134 Share on other sites More sharing options...
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