Amortization schedule (area)

_.md

[ Launch: Amortization schedule ] 8850760 by poezn
[ Launch: Amortization schedule ] 8365957 by poezn

assets.svg

config.json

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inlet.js

// A = i x P x ((1+i)^n)/(1+i)^n - 1
// A = monthly payment
// P = initial principal
// i = monthly interest rate
// n = number of payments


// ==================================
// HERE. THIS DATA CHANGES EVERYTHING
var apr = 5.90000000000001; // in percent
var term = 35; // in years 
var p = 303122;
// ALRIGHT WE'RE DONE
// ==================================


var i = apr / 1200;
var n = term * 12;
var monthlyPayment = i * p * Math.pow((1+i), n) / (Math.pow((1+i), n) - 1);

var schedule = [];
var balance = p;

for (var j = 0; j < n; j++) {
  var paidInterest = balance * i;
  var paidPrincipal = monthlyPayment - paidInterest;
  var balance = balance - paidPrincipal;
  schedule.push({
    amount: monthlyPayment,
    paidPrincipal: paidPrincipal,
    paidInterest: paidInterest,
    balance: balance
  })
}

// =========
var w = 525,
    h = 200;

var scale = d3.scale.linear()
.domain([0, monthlyPayment])
.range([h, 0]);

var widthScale = d3.scale.linear()
.domain([0, schedule.length])
.range([0, w]);


var format = d3.format("4.2f");

  var g = d3.select("#graph");

var renderInterest = function(d, idx) {
  var barScale = d3.scale.linear()
  .domain([0, d.amount])
  .range([0, h]);

  console.log(d);
  var data = [
    d.paidInterest,
    d.paidPrincipal
  ];
  
  var rects = d3.select("#overlays").selectAll("rect.bar")
  .data(data);
  
  rects.enter().append("rect")
  .attr({
    "class": function(d, i) {
      return "bar " + (i === 0 ? "interest" : "principal");
    },
    "stroke": "#FFFFFF",
    "stroke-opacity": 0.1,
    "stroke-width": 2
  });
  
  rects.attr({
    "transform": function(d, i) {
      var tx = widthScale(idx) - 10,
          ty = (i === 0 ? h - barScale(d) : 0);
      return "translate(" + [tx, ty].join(" ") + ")"
    },
    "width": 20,
    "height": function(d, i) {
      return barScale(d)
    }  
  });
  
  d3.select("#monthid")
  .text("Month " + (idx+1) + "/" + n);

  d3.select("text.interest")
  .text("Interest: $" + format(d.paidInterest));

  d3.select("text.principal")
  .text("Principal: $" + format(d.paidPrincipal));

  d3.select("#monthlypayment")
  .text("Monthly Payment: $" + format(monthlyPayment));
  
  d3.selectAll(".shadow, #overlays line")
  .attr({
    "transform": function(d, i) {
      var tx = -10 + widthScale(idx)
      return "translate(" + tx + " -3)"
    }
  })

};

var interestArea = d3.svg.area()
.x(function(d, i) {
  return widthScale(i);
})
.y(function(d, i) {
  return scale(d.paidInterest);
})
.y0(h);

var principalArea = d3.svg.area()
.x(function(d, i) {
  return widthScale(i);
})
.y(function(d, i) {
  return scale(d.paidInterest);
})
.y0(0);

var area = g.selectAll(".area")
.data([
  {
    "path": interestArea(schedule),
    "type": "interest"
  }, {
    "path": principalArea(schedule),
    "type": "principal"
  }
]);

area.enter().append("path");

area.attr({
  "d": function(d, i) {
    return d.path;
  },
  "class": function(d, i) {
    return "area " + d.type;
  }
})
.on("mousemove", function(ev) {
  var mouse = d3.mouse(this);
  var xPos = mouse[0];
  var idx = Math.round(widthScale.invert(xPos));
  renderInterest(schedule[idx], idx);
});


renderInterest(schedule[0], 0);

styles.css

text {
  font-size: 14px;
  font-family: "Helvetica Neue", Helvetica, sans-serif
}

.interest {
  fill: #CC7EAA;
}

.principal {
  fill: #7E83CC;
}

rect.interest {
  fill: #CC3289;
}

rect.principal {
  fill: #404ACE;
}