diff --git a/lib/bcoin/tx.js b/lib/bcoin/tx.js
index 896455a1..a25a09b7 100644
--- a/lib/bcoin/tx.js
+++ b/lib/bcoin/tx.js
@@ -18,7 +18,6 @@ function TX(data, block) {
   this.lock = data.lock || 0;
   this.ts = data.ts || 0;
   this.block = null;
-  this.funds = new bn(0);
 
   this._hash = null;
   this._raw = data._raw || null;
@@ -94,8 +93,6 @@ TX.prototype._input = function _input(i, index) {
     ex.script = input.script.length ? input.script : ex.script;
   } else {
     this.inputs.push(input);
-    if (input.out.tx)
-      this.funds.iadd(input.out.tx.outputs[input.out.index].value);
     index = this.inputs.length - 1;
   }
 
@@ -250,6 +247,35 @@ TX.prototype.inputAddrs = function inputAddrs() {
   });
 };
 
+TX.prototype.funds = function funds(side) {
+  if (side === 'in') {
+    var inputs = this.inputs.filter(function(input) {
+      return input.out.tx;
+    });
+
+    var acc = new bn(0);
+    if (inputs.length === 0)
+      return acc;
+
+    inputs.reduce(function(acc, input) {
+      return acc.iadd(input.out.tx.outputs[input.out.index].value);
+    }, acc);
+
+    return acc;
+  }
+
+  // Output
+  var acc = new bn(0);
+  if (this.outputs.length === 0)
+    return acc;
+
+  this.outputs.reduce(function(acc, output) {
+    return acc.iadd(output.value);
+  }, acc);
+
+  return acc;
+};
+
 TX.prototype.toJSON = function toJSON() {
   // Compact representation
   return {
diff --git a/lib/bcoin/wallet.js b/lib/bcoin/wallet.js
index 42904a2c..82c90f68 100644
--- a/lib/bcoin/wallet.js
+++ b/lib/bcoin/wallet.js
@@ -1,6 +1,7 @@
 var assert = require('assert');
 var bcoin = require('../bcoin');
 var hash = require('hash.js');
+var bn = require('bn.js');
 var util = require('util');
 var EventEmitter = require('events').EventEmitter;
 var utils = bcoin.utils;
@@ -39,6 +40,11 @@ function Wallet(options, passphrase) {
 
   this.prefix = 'bt/' + this.getAddress() + '/';
   this.tx = new bcoin.txPool(this);
+
+  // Just a constants, actually
+  this.fee = 10000;
+  this.dust = 5460;
+
   this._init();
 }
 util.inherits(Wallet, EventEmitter);
@@ -241,6 +247,76 @@ Wallet.prototype.balance = function balance() {
   return this.tx.balance();
 };
 
+Wallet.prototype.fill = function fill(tx, cb) {
+  // NOTE: tx should be prefilled with all outputs
+  var cost = tx.funds('out');
+
+  // Use initial fee for starters
+  var fee = 1;
+
+  // total = cost + fee
+  var total = cost.add(new bn(this.fee));
+
+  var lastAdded = -1;
+  function addInput(unspent, i) {
+    // Add new inputs until TX will have enough funds to cover both
+    // minimum post cost and fee
+    tx.input(unspent);
+    lastAdded = i;
+    return tx.funds('in').cmp(total) < 0;
+  }
+
+  // Transfer `total` funds maximum
+  var unspent = this.unspent();
+  unspent.every(addInput, this);
+
+  // Add dummy output (for `left`) to calculate maximum TX size
+  tx.out(this, new bn(0));
+
+  // Change fee value if it is more than 1024 bytes
+  // (10000 satoshi for every 1024 bytes)
+  do {
+    // Calculate maximum possible size after signing
+    var byteSize = tx.maxSize();
+
+    var addFee = Math.ceil(byteSize / 1024) - fee;
+    total.iadd(new bn(addFee * this.fee));
+    fee += addFee;
+
+    // Failed to get enough funds, add more inputs
+    if (tx.funds('in').cmp(total) < 0)
+      unspent.slice(lastAdded + 1).every(addInput, this);
+  } while (tx.funds('in').cmp(total) < 0 && lastAdded < unspent.length);
+
+  // Still failing to get enough funds, notify caller
+  if (tx.funds('in').cmp(total) < 0) {
+    var err = new Error('Not enough funds');
+    err.minBalance = total;
+    return cb(err);
+  }
+
+  // How much money is left after sending outputs
+  var left = tx.funds('in').sub(total);
+
+  // Not enough money, transfer everything to owner
+  if (left.cmpn(this.dust) < 0) {
+    // NOTE: that this output is either `postCost` or one of the `dust` values
+    tx.outputs[tx.outputs.length - 2].value.iadd(left);
+    left = new bn(0);
+  }
+
+  // Change or remove last output if there is some money left
+  if (left.cmpn(0) === 0)
+    tx.outputs.pop();
+  else
+    tx.outputs[tx.outputs.length - 1].value = left;
+
+  // Sign transaction
+  this.sign(tx);
+
+  return tx;
+};
+
 Wallet.prototype.toJSON = function toJSON() {
   return {
     v: 1,
diff --git a/test/wallet-test.js b/test/wallet-test.js
index f84b32bc..fb200a37 100644
--- a/test/wallet-test.js
+++ b/test/wallet-test.js
@@ -130,4 +130,23 @@ describe('Wallet', function() {
       return tx.hash('hex') === f1.hash('hex');
     }));
   });
+
+  it('should fill tx with inputs', function() {
+    var w1 = bcoin.wallet();
+    var w2 = bcoin.wallet();
+
+    // Coinbase
+    var t1 = bcoin.tx().out(w1, 5460).out(w1, 5460).out(w1, 5460).out(w1, 5460);
+
+    // Fake TX should temporarly change output
+    w1.addTX(t1);
+
+    // Create new transaction
+    var t2 = bcoin.tx().out(w2, 5460);
+    w1.sign(t2);
+    w1.fill(t2);
+
+    assert.equal(t2.funds('in').toString(10), 16380);
+    assert.equal(t2.funds('out').toString(10), 6380);
+  });
 });