diff --git a/src/networks.js b/src/networks.js
index fdb3706..eedb66a 100644
--- a/src/networks.js
+++ b/src/networks.js
@@ -1,6 +1,11 @@
 // https://en.bitcoin.it/wiki/List_of_address_prefixes
 // Dogecoin BIP32 is a proposed standard: https://bitcointalk.org/index.php?topic=409731
-module.exports = {
+
+function bitcoinEstimateFee(txByteSize) {
+  return networks.bitcoin.feePerKb * Math.ceil(txByteSize / 1000)
+}
+
+var networks = {
   bitcoin: {
     magicPrefix: '\x18Bitcoin Signed Message:\n',
     bip32: {
@@ -10,8 +15,9 @@ module.exports = {
     pubKeyHash: 0x00,
     scriptHash: 0x05,
     wif: 0x80,
-    dustThreshold: 546,
-    feePerKb: 10000
+    dustThreshold: 546, // https://github.com/bitcoin/bitcoin/blob/529047fcd18acd1b64dc95d6eb69edeaad75d405/src/core.h#L176-L188
+    feePerKb: 10000, // https://github.com/bitcoin/bitcoin/blob/3f39b9d4551d729c3a2e4decd810ac6887cfaeb3/src/main.cpp#L52
+    estimateFee: bitcoinEstimateFee
   },
   dogecoin: {
     magicPrefix: '\x19Dogecoin Signed Message:\n',
@@ -47,6 +53,8 @@ module.exports = {
     scriptHash: 0xc4,
     wif: 0xef,
     dustThreshold: 546,
-    feePerKb: 10000
+    feePerKb: 10000,
+    estimateFee: bitcoinEstimateFee
   }
 }
+module.exports = networks
diff --git a/src/wallet.js b/src/wallet.js
index 1e484f2..b15bcfd 100644
--- a/src/wallet.js
+++ b/src/wallet.js
@@ -237,7 +237,7 @@ function Wallet(seed, network) {
     tmpTx.addOutput(getChangeAddress(), 0)
 
     var byteSize = tmpTx.toBuffer().length
-    return network.feePerKb * Math.ceil(byteSize / 1000)
+    return network.estimateFee(byteSize)
   }
 
   function getChangeAddress() {
diff --git a/test/network.js b/test/network.js
new file mode 100644
index 0000000..ee0d6d4
--- /dev/null
+++ b/test/network.js
@@ -0,0 +1,23 @@
+var assert = require('assert')
+var networks = require('../src/networks')
+var Transaction = require('../src/transaction')
+
+var fixtureTxes = require('./fixtures/mainnet_tx')
+var fixtureTx1Hex = fixtureTxes.prevTx
+var fixtureTxBigHex = fixtureTxes.bigTx
+
+describe('bitcoin', function() {
+  describe('estimateFee', function() {
+    var estimateFee = networks.bitcoin.estimateFee
+
+    it('works for fixture tx 1', function() {
+      var tx = Transaction.fromHex(fixtureTx1Hex)
+      assert.equal(estimateFee(tx.toBuffer().length), 10000)
+    })
+
+    it('works for fixture big tx', function() {
+      var tx = Transaction.fromHex(fixtureTxBigHex)
+      assert.equal(estimateFee(tx.toBuffer().length), 30000)
+    })
+  })
+})