diff --git a/src/santander_check_number_validator.js b/src/santander_check_number_validator.js
new file mode 100644
index 0000000..b4ba836
--- /dev/null
+++ b/src/santander_check_number_validator.js
@@ -0,0 +1,35 @@
+(function(window) {
+  var Moip = window.Moip || {};
+  window.Moip = Moip;
+
+  function SantanderCheckNumberCalculator() {
+    if ( !( this instanceof SantanderCheckNumberCalculator ) ) {
+      return new SantanderCheckNumberCalculator();
+    }
+  }
+
+  SantanderCheckNumberCalculator.prototype = {
+
+    calculateAccount: function(agencyNumber,accountNumber) {
+      var numbers = (agencyNumber + "00" + accountNumber).split("");
+      var sumSeq = 0;
+      
+      for (var i = 0; i < numbers.length; i++) {
+        var number = parseInt(numbers[i]);
+        sumSeq += this.multiplyAccordingWeight(number, i);
+      }
+      sumSeq = parseInt(sumSeq.toString().substr(-1));
+      if ( sumSeq === 0 ) return "0";
+      else return (10 - sumSeq).toString();
+    },
+
+    multiplyAccordingWeight: function(number, index) {
+      var weight = [9,7,3,1,0,0,9,7,1,3,1,9,7,3];
+      var res = number * weight[index];
+      return parseInt(res.toString().substr(-1))
+    }
+  };
+
+  Moip.SantanderCheckNumberCalculator = SantanderCheckNumberCalculator();
+
+})(window);
\ No newline at end of file
diff --git a/src/santander_validator.js b/src/santander_validator.js
index 544c2d7..2396d55 100644
--- a/src/santander_validator.js
+++ b/src/santander_validator.js
@@ -31,7 +31,8 @@
     },
     
     accountCheckNumberMatch: function(bankAccount) {
-      return true;
+      var checkNumberCalculated = Moip.SantanderCheckNumberCalculator.calculateAccount(bankAccount.agencyNumber,bankAccount.accountNumber);
+      return checkNumberCalculated === bankAccount.accountCheckNumber.toUpperCase();
     },
 
     agencyNumberMsgError: function() {