diff --git a/lib/boleto.js b/lib/boleto.js
index 5eb2b53..e12c210 100644
--- a/lib/boleto.js
+++ b/lib/boleto.js
@@ -4,13 +4,13 @@ const barcode = require('./barcode')
 const path = require('path')
 const moment = require('moment')
 
-var banks = null
+let banks = null
 
-var hashString = function (string) {
-  var hash = 0
-  var i
-  var chr
-  var len
+const hashString = function (string) {
+  let hash = 0
+  let i
+  let chr
+  let len
 
   if (string.length == 0) return hash
   for (i = 0, len = string.length; i < len; i++) {
@@ -21,7 +21,7 @@ var hashString = function (string) {
   return hash
 }
 
-var Boleto = function (options) {
+const Boleto = function (options) {
   if (!options) {
     throw 'No options provided initializing Boleto.'
   }
@@ -43,7 +43,7 @@ var Boleto = function (options) {
     options['data_vencimento'] = moment(moment(options['data_vencimento']).utc().format('YYYY-MM-DD'))
   }
 
-  for (var key in options) {
+  for (let key in options) {
     this[key] = options[key]
   }
 
@@ -67,13 +67,13 @@ Boleto.prototype._calculate = function () {
 }
 
 Boleto.prototype.renderHTML = function (callback) {
-  var self = this
+  const self = this
 
-  var renderOptions = self.bank.options
+  let renderOptions = self.bank.options
   renderOptions.boleto = self
 
   // Copy renderHelper's methods to renderOptions
-  for (var key in formatters) {
+  for (let key in formatters) {
     renderOptions[key] = formatters[key]
   }
 
diff --git a/lib/edi-helper.js b/lib/edi-helper.js
index 991cf1d..39d5aaf 100644
--- a/lib/edi-helper.js
+++ b/lib/edi-helper.js
@@ -1,4 +1,4 @@
-var crypto = require('crypto')
+const crypto = require('crypto')
 
 exports.calculateLineChecksum = function (line) {
   return crypto.createHash('sha1').update(line).digest('hex')
diff --git a/lib/formatters.js b/lib/formatters.js
index 62286a9..6aa4511 100644
--- a/lib/formatters.js
+++ b/lib/formatters.js
@@ -17,13 +17,15 @@ exports.addTrailingZeros = function (string, length) {
 
 exports.formatAmount = function (amount) {
   amount = amount.toString()
-  var cents = exports.addTrailingZeros(amount.substring(amount.length - 2, amount.length), 2)
-  var integers = exports.addTrailingZeros(amount.substring(0, amount.length - 2), 1)
+  const cents = exports.addTrailingZeros(amount.substring(amount.length - 2, amount.length), 2)
+  let integers = exports.addTrailingZeros(amount.substring(0, amount.length - 2), 1)
 
-  var newIntegers = ''
+  let newIntegers = ''
+  let len
+  let i
 
-  for (var i = 0; i < integers.length; i++) {
-    if (i > 0 && (integers.length - i) % 3 == 0) newIntegers += '.'
+  for (i = 0, len = integers.length; i < len; i++) {
+    if (i > 0 && (len - i) % 3 == 0) newIntegers += '.'
     newIntegers += integers[i]
   }
 
@@ -38,11 +40,11 @@ exports.mod11 = function (num, base, r) {
   if (!base) base = 9
   if (!r) r = 0
 
-  var soma = 0
-  var fator = 2
+  let soma = 0
+  let fator = 2
 
-  for (var i = num.length - 1; i >= 0; i--) {
-    var parcial = parseInt(num[i]) * fator
+  for (let i = num.length - 1; i >= 0; i--) {
+    const parcial = parseInt(num[i]) * fator
     soma += parcial
 
     if (fator == base) {
@@ -54,7 +56,7 @@ exports.mod11 = function (num, base, r) {
 
   if (r == 0) {
     soma *= 10
-    var digito = soma % 11
+    const digito = soma % 11
     return digito == 10 ? 0 : digito
   } else if (r == 1) {
     return soma % 11
@@ -62,20 +64,20 @@ exports.mod11 = function (num, base, r) {
 }
 
 exports.mod10 = function (num) {
-  var total = 0
-  var fator = 2
+  let total = 0
+  let fator = 2
 
-  for (var i = num.length - 1; i >= 0; i--) {
-    var temp = (parseInt(num[i]) * fator).toString()
-    var tempSum = 0
-    for (var j = 0; j < temp.length; j++) {
+  for (let i = num.length - 1; i >= 0; i--) {
+    let temp = (parseInt(num[i]) * fator).toString()
+    let tempSum = 0
+    for (let j = 0; j < temp.length; j++) {
       tempSum += parseInt(temp[j])
     }
     total += tempSum
     fator = (fator == 2) ? 1 : 2
   }
 
-  var resto = total % 10
+  const resto = total % 10
   return (resto == 0) ? 0 : (10 - resto)
 }