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+# surcharge-calculator
+
+![](https://img.shields.io/badge/written%20in-Javascript-blue)
+
+Determine what surcharge is worth paying in order to offset a loan.
+
+
+## Download
+
+- [⬇️ surcharge-calculator.html](dist-archive/surcharge-calculator.html) *(1.88 KiB)*
diff --git a/dist-archive/surcharge-calculator.html b/dist-archive/surcharge-calculator.html
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+<!DOCTYPE html>
+<html>
+	<head>
+		<meta charset="UTF-8">
+	</head>
+	<body>
+
+		<div id="config-area">
+			Surcharge: <input type="number" min="0" value="2" id="surcharge-percent">%
+			<br>
+			Debt rate: <input type="number" min="0" value="5" id="debt-percent">% p.a.
+			<br>
+			Reward rate: <input type="number" min="0" value="0" id="reward-percent">%
+			<br>
+			Debt compounding period: <input type="number" min="1" value="1" id="compounding-period"> Day(s)
+			<br>
+			Interest free days: <input type="number" min="1" value="30" id="interest-free-days"> Day(s)
+		</div>
+		
+		<hr>
+		
+		<div id="output" style="white-space:pre;">
+		</div>
+	
+		<script type="text/javascript">
+function $(query) {
+	return document.querySelector(query);
+}
+		
+function output(sz) {
+	$("#output").textContent = sz;
+}
+		
+function recalculate() {
+	var S = + $("#surcharge-percent").value;
+	var D = + $("#debt-percent").value;
+	var R = + $("#reward-percent").value;
+	var T = + $("#compounding-period").value;
+	var P = + $("#interest-free-days").value;
+	
+	// @ref http://money.stackexchange.com/questions/72654/what-credit-card-surcharge-rate-should-i-accept 
+	
+	var lhs = (1 + (S - R)/100); // net expense of the surcharge minus the rewards
+	var rhs = (1 + ((T/365)*D/100)) ** P; // interest that you would pay otherwise
+	
+	var ret = "DECISION: ";
+	if (lhs < rhs) {
+		ret += "Better to use CREDIT.";
+	} else if (lhs > rhs) {
+		ret += "Better to use DEBIT.";
+	} else {
+		ret += "No difference.";
+	}
+	ret += "\n\n";
+	ret += "Net expense of (surcharge minus rewards): " + lhs + "\n";
+	ret += "Interest that you would pay otherwise: " + rhs + "\n";
+	
+	output(ret);
+}
+
+function setup() {
+	var items = document.querySelectorAll("#config-area input");
+	for (var i = 0; i < items.length; ++i) {
+		items[i].addEventListener('change', recalculate);
+		items[i].addEventListener('keyup', recalculate);
+	}
+	recalculate();
+}
+
+setup();
+
+		</script>	
+	</body>
+</html>
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