diff --git a/lib/model/txproposal.js b/lib/model/txproposal.js
index 3209246..5a05b00 100644
--- a/lib/model/txproposal.js
+++ b/lib/model/txproposal.js
@@ -171,10 +171,9 @@ TxProposal.prototype.getRawTx = function() {
   return t.uncheckedSerialize();
 };
 
-TxProposal.prototype.estimateFee = function() {
+TxProposal.prototype.getEstimatedSize = function() {
   // Note: found empirically based on all multisig P2SH inputs and within m & n allowed limits.
   var safetyMargin = 0.05;
-
   var walletM = this.requiredSignatures;
 
   var overhead = 4 + 4 + 9 + 9;
@@ -185,7 +184,13 @@ TxProposal.prototype.estimateFee = function() {
 
   var size = overhead + inputSize * nbInputs + outputSize * nbOutputs;
 
-  var fee = this.feePerKb * (size * (1 + safetyMargin)) / 1000;
+  return parseInt((size * (1 + safetyMargin)).toFixed(0));
+};
+
+TxProposal.prototype.estimateFee = function() {
+
+  var size = this.getEstimatedSize();
+  var fee = this.feePerKb * size / 1000;
 
   // Round up to nearest bit
   this.fee = parseInt((Math.ceil(fee / 100) * 100).toFixed(0));
diff --git a/lib/server.js b/lib/server.js
index 6672769..e4218bf 100644
--- a/lib/server.js
+++ b/lib/server.js
@@ -692,7 +692,7 @@ WalletService.prototype._totalizeUtxos = function(utxos) {
 };
 
 
-WalletService.prototype._computeKbToSendMax = function(utxos, amount, cb) {
+WalletService.prototype._computeBytesToSendMax = function(utxos, cb) {
   var self = this;
 
   var unlockedUtxos = _.reject(utxos, 'locked');
@@ -701,17 +701,16 @@ WalletService.prototype._computeKbToSendMax = function(utxos, amount, cb) {
   self.getWallet({}, function(err, wallet) {
     if (err) return cb(err);
 
-    var t = WalletUtils.newBitcoreTransaction();
-    try {
-      _.each(unlockedUtxos, function(i) {
-        t.from(i, i.publicKeys, wallet.m);
-      });
-      t.to(utxos[0].address, amount);
-      var sizeInKb = Math.ceil(t._estimateSize() / 1000);
-      return cb(null, sizeInKb);
-    } catch (ex) {
-      return cb(ex);
-    }
+    var txp = Model.TxProposal.create({
+      walletId: self.walletId,
+      requiredSignatures: wallet.m,
+      walletN: wallet.n,
+    });
+    txp.inputs = unlockedUtxos;
+
+    var size = txp.getEstimatedSize();
+
+    return cb(null, size);
   });
 };
 
@@ -744,11 +743,11 @@ WalletService.prototype.getBalance = function(opts, cb) {
 
     balance.byAddress = _.values(byAddress);
 
-    self._computeKbToSendMax(utxos, balance.availableAmount, function(err, sizeInKb) {
+    self._computeBytesToSendMax(utxos, function(err, sizeInBytes) {
       if (err) {
         log.error('Could not compute fees needed to transfer max amount', err);
       }
-      balance.totalKbToSendMax = sizeInKb || 0;
+      balance.totalBytesToSendMax = sizeInBytes || 0;
       return cb(null, balance);
     });
   });
diff --git a/test/integration/server.js b/test/integration/server.js
index 6162f2d..6770ae0 100644
--- a/test/integration/server.js
+++ b/test/integration/server.js
@@ -1370,7 +1370,7 @@ describe('Wallet service', function() {
           balance.totalAmount.should.equal(helpers.toSatoshi(6));
           balance.lockedAmount.should.equal(0);
           balance.availableAmount.should.equal(helpers.toSatoshi(6));
-          balance.totalKbToSendMax.should.equal(1);
+          balance.totalBytesToSendMax.should.equal(578);
 
           balance.totalConfirmedAmount.should.equal(helpers.toSatoshi(4));
           balance.lockedConfirmedAmount.should.equal(0);
@@ -1396,7 +1396,7 @@ describe('Wallet service', function() {
         balance.totalAmount.should.equal(0);
         balance.lockedAmount.should.equal(0);
         balance.availableAmount.should.equal(0);
-        balance.totalKbToSendMax.should.equal(0);
+        balance.totalBytesToSendMax.should.equal(0);
         should.exist(balance.byAddress);
         balance.byAddress.length.should.equal(0);
         done();
@@ -1412,7 +1412,7 @@ describe('Wallet service', function() {
           balance.totalAmount.should.equal(0);
           balance.lockedAmount.should.equal(0);
           balance.availableAmount.should.equal(0);
-          balance.totalKbToSendMax.should.equal(0);
+          balance.totalBytesToSendMax.should.equal(0);
           should.exist(balance.byAddress);
           balance.byAddress.length.should.equal(0);
           done();
@@ -1440,7 +1440,7 @@ describe('Wallet service', function() {
           should.exist(balance);
           balance.totalAmount.should.equal(helpers.toSatoshi(9));
           balance.lockedAmount.should.equal(0);
-          balance.totalKbToSendMax.should.equal(2);
+          balance.totalBytesToSendMax.should.equal(1535);
           done();
         });
       });
@@ -2093,18 +2093,21 @@ describe('Wallet service', function() {
           balance.totalAmount.should.equal(helpers.toSatoshi(9));
           balance.lockedAmount.should.equal(0);
           balance.availableAmount.should.equal(helpers.toSatoshi(9));
-          balance.totalKbToSendMax.should.equal(3);
-          var max = (balance.totalAmount - balance.lockedAmount) - (balance.totalKbToSendMax * 10000);
+          balance.totalBytesToSendMax.should.equal(2896);
+          var sizeInKB = balance.totalBytesToSendMax / 1000;
+          var fee = parseInt((Math.ceil(sizeInKB * 10000 / 100) * 100).toFixed(0));
+          var max = balance.availableAmount - fee;
           var txOpts = helpers.createSimpleProposalOpts('18PzpUFkFZE8zKWUPvfykkTxmB9oMR8qP7', max / 1e8, null, TestData.copayers[0].privKey_1H_0);
           server.createTx(txOpts, function(err, tx) {
             should.not.exist(err);
             should.exist(tx);
             tx.amount.should.equal(max);
-            var estimatedFee = 2900 * 10000 / 1000; // estimated size = 2900 bytes
+            var estimatedFee = 2896 * 10000 / 1000;
             tx.fee.should.be.within(0.9 * estimatedFee, 1.1 * estimatedFee);
             server.getBalance({}, function(err, balance) {
               should.not.exist(err);
               balance.lockedAmount.should.equal(helpers.toSatoshi(9));
+              balance.availableAmount.should.equal(0);
               done();
             });
           });
@@ -2121,14 +2124,16 @@ describe('Wallet service', function() {
             balance.totalAmount.should.equal(helpers.toSatoshi(9));
             balance.lockedAmount.should.equal(helpers.toSatoshi(4));
             balance.availableAmount.should.equal(helpers.toSatoshi(5));
-            balance.totalKbToSendMax.should.equal(2);
-            var max = (balance.totalAmount - balance.lockedAmount) - (balance.totalKbToSendMax * 2000);
+            balance.totalBytesToSendMax.should.equal(1653);
+            var sizeInKB = balance.totalBytesToSendMax / 1000;
+            var fee = parseInt((Math.ceil(sizeInKB * 2000 / 100) * 100).toFixed(0));
+            var max = balance.availableAmount - fee;
             var txOpts = helpers.createSimpleProposalOpts('18PzpUFkFZE8zKWUPvfykkTxmB9oMR8qP7', max / 1e8, null, TestData.copayers[0].privKey_1H_0, 2000);
             server.createTx(txOpts, function(err, tx) {
               should.not.exist(err);
               should.exist(tx);
               tx.amount.should.equal(max);
-              var estimatedFee = 1650 * 2000 / 1000; // estimated size = 1650 bytes
+              var estimatedFee = 1653 * 2000 / 1000;
               tx.fee.should.be.within(0.9 * estimatedFee, 1.1 * estimatedFee);
               server.getBalance({}, function(err, balance) {
                 should.not.exist(err);