diff --git a/package.json b/package.json
index 4e334e4..1465b06 100644
--- a/package.json
+++ b/package.json
@@ -9,14 +9,14 @@
     "lint": "next lint"
   },
   "dependencies": {
-    "@cashscript/utils": "^0.13.1",
+    "@cashscript/utils": "^0.14.0-next.1",
     "@emotion/react": "^11.14.0",
     "@emotion/styled": "^11.14.0",
     "@monaco-editor/react": "^4.7.0",
     "bootstrap": "^5.3.7",
-    "cashc": "^0.13.1",
+    "cashc": "^0.14.0-next.1",
     "cashc-v0.12": "npm:cashc@^0.12.2",
-    "cashscript": "^0.13.1",
+    "cashscript": "^0.14.0-next.1",
     "next": "15.5.9",
     "react": "18.2.0",
     "react-bootstrap": "^2.10.10",
diff --git a/src/components/Editor.tsx b/src/components/Editor.tsx
index 1dc1cb6..d5b31e9 100644
--- a/src/components/Editor.tsx
+++ b/src/components/Editor.tsx
@@ -94,7 +94,7 @@ const Editor: React.FC<Props> = ({ code, setCode, compile, compilerVersion, setC
           onChange={(e) => setCompilerVersion(e.target.value as CashScriptVersion)}
           style={{ width: '170px', borderRadius: '30px' }}
         >
-          <option value="0.13">cashc v0.13</option>
+          <option value="0.14">cashc v0.14</option>
           <option value="0.12">cashc v0.12</option>
         </Form.Select>
         <Button
diff --git a/src/components/Main.tsx b/src/components/Main.tsx
index f4f5496..0b4c7f5 100644
--- a/src/components/Main.tsx
+++ b/src/components/Main.tsx
@@ -28,7 +28,7 @@ const Main: React.FC<Props> = ({
 }) => {
 
   const [initializeContracts, setInitializeContracts] = useState<0 | 1 | 2>(0);
-  const [compilerVersion, setCompilerVersion] = useState<CashScriptVersion>('0.13');
+  const [compilerVersion, setCompilerVersion] = useState<CashScriptVersion>('0.14');
 
   useEffect(() => {
     const codeLocalStorage = localStorage.getItem("code");
@@ -44,10 +44,10 @@ const Main: React.FC<Props> = ({
     } else {
       // add default example contracts to local storage
       try {
-        const artifactExampleTimeout = compileCashScript(exampleTimeoutContract, '0.13')
-        const artifactExampleEscrow = compileCashScript(exampleEscrowContract, '0.13')
-        const artifactExampleStramingMecenas = compileCashScript(exampleStramingMecenasContract, '0.13')
-        const artifactExampleDex = compileCashScript(exampleDexContract, '0.13')
+        const artifactExampleTimeout = compileCashScript(exampleTimeoutContract, '0.14')
+        const artifactExampleEscrow = compileCashScript(exampleEscrowContract, '0.14')
+        const artifactExampleStramingMecenas = compileCashScript(exampleStramingMecenasContract, '0.14')
+        const artifactExampleDex = compileCashScript(exampleDexContract, '0.14')
         const defaultArtifacts = [artifactExampleTimeout, artifactExampleEscrow, artifactExampleStramingMecenas, artifactExampleDex]
         setArtifacts(defaultArtifacts)
         localStorage.setItem("artifacts", JSON.stringify(defaultArtifacts, null, 2));
diff --git a/src/components/TransactionBuilder.tsx b/src/components/TransactionBuilder.tsx
index 7d2537f..7766a76 100644
--- a/src/components/TransactionBuilder.tsx
+++ b/src/components/TransactionBuilder.tsx
@@ -1,4 +1,4 @@
-import React, {useState} from 'react'
+import React, {useState, useCallback, useMemo} from 'react'
 import { NetworkProvider, Output, SignatureTemplate, TransactionBuilder, Unlocker } from 'cashscript'
 import { Wallet, ContractInfo, ExplorerString, ContractUtxo, WalletUtxo } from './shared'
 import { Button, Card, Form } from 'react-bootstrap'
@@ -48,32 +48,51 @@ const TransactionBuilderPage: React.FC<Props> = ({ provider, wallets, contracts,
     setInputs(inputsCopy)
   }
 
-  async function sendTransaction() {  
-    // try to send transaction and alert result
+  // Construct a TransactionBuilder from the current inputs, outputs and options.
+  // Shared by sendTransaction and the live fee calculation. Throws if the
+  // transaction is incomplete (e.g. an undefined input or missing unlocker).
+  const buildTransaction = useCallback(() => {
+    // start constructing transaction
+    const transaction = new TransactionBuilder({
+      provider,
+      allowImplicitFungibleTokenBurn,
+      ...(enableMaxFeeSatoshis && maximumFeeSatoshis ? { maximumFeeSatoshis: BigInt(maximumFeeSatoshis) } : {}),
+      ...(enableMaxFeeSatsPerByte && maximumFeeSatsPerByte ? { maximumFeeSatsPerByte: Number(maximumFeeSatsPerByte) } : {}),
+    })
+
+    // add inputs to transaction in the user-defined order
+    inputs.forEach((input, inputIndex) => {
+      if(!input) throw new Error("Undefined input provided")
+      if('walletIndex' in input){
+        const walletIndex = input.walletIndex
+        const sigTemplate = new SignatureTemplate(wallets[walletIndex].privKey)
+        transaction.addInput(input, sigTemplate.unlockP2PKH())
+      } else {
+        const inputUnlocker = inputUnlockers[inputIndex]
+        if(!inputUnlocker) throw new Error("Missing unlocker for input")
+        transaction.addInput(input, inputUnlocker)
+      }
+    })
+
+    transaction.addOutputs(outputs)
+    if(enableLocktime) transaction.setLocktime(Number(locktime))
+    return transaction
+  }, [provider, wallets, allowImplicitFungibleTokenBurn, enableMaxFeeSatoshis, maximumFeeSatoshis, enableMaxFeeSatsPerByte, maximumFeeSatsPerByte, inputs, inputUnlockers, outputs, enableLocktime, locktime])
+
+  // Reactively calculate the transaction fee and fee rate as the user edits the
+  // inputs/outputs. Returns null while the transaction can't yet be built.
+  const feeData = useMemo(() => {
     try {
-      // start constructing transaction
-      const transaction = new TransactionBuilder({
-        provider,
-        allowImplicitFungibleTokenBurn,
-        ...(enableMaxFeeSatoshis && maximumFeeSatoshis ? { maximumFeeSatoshis: BigInt(maximumFeeSatoshis) } : {}),
-        ...(enableMaxFeeSatsPerByte && maximumFeeSatsPerByte ? { maximumFeeSatsPerByte: Number(maximumFeeSatsPerByte) } : {}),
-      })
-
-      // add inputs to transaction in the user-defined order
-      inputs.forEach((input, inputIndex) => {
-        if(!input) throw new Error("Undefined input provided")
-        if('walletIndex' in input){
-          const walletIndex = input.walletIndex
-          const sigTemplate = new SignatureTemplate(wallets[walletIndex].privKey)
-          transaction.addInput(input, sigTemplate.unlockP2PKH())
-        } else {
-          const inputUnlocker = inputUnlockers[inputIndex]
-          transaction.addInput(input, inputUnlocker)
-        }
-      })
+      return buildTransaction().calculateTransactionFee()
+    } catch {
+      return null
+    }
+  }, [buildTransaction])
 
-      transaction.addOutputs(outputs)
-      if(enableLocktime) transaction.setLocktime(Number(locktime))
+  async function sendTransaction() {
+    // try to send transaction and alert result
+    try {
+      const transaction = buildTransaction()
 
       // check for mocknet
       if(provider.network == "mocknet"){
@@ -205,6 +224,19 @@ const TransactionBuilderPage: React.FC<Props> = ({ provider, wallets, contracts,
         </Form>
       </details>
 
+      <div style={{ marginBottom: '10px' }}>
+        {feeData ? (
+          <span>
+            Calculated fee: <strong>{feeData.feeSats.toString()} sats</strong>
+            {' '}(<strong>{feeData.feeSatsPerByte.toFixed(2)} sats/byte</strong>)
+          </span>
+        ) : (
+          <span style={{ color: '#888' }}>
+            Calculated fee: add valid inputs and outputs to calculate the fee
+          </span>
+        )}
+      </div>
+
       <Button variant="secondary" style={{ display: "block" }} size="sm" onClick={sendTransaction}>
         { provider.network === "mocknet" ? "Evaluate" : "Send" }
       </Button>
diff --git a/src/editor/cashscript/diagnostics.ts b/src/editor/cashscript/diagnostics.ts
index 4a407a5..29e79cb 100644
--- a/src/editor/cashscript/diagnostics.ts
+++ b/src/editor/cashscript/diagnostics.ts
@@ -62,7 +62,7 @@ export interface CashScriptDiagnostic {
 }
 
 const compileStringByVersion: Record<CashScriptVersion, CompileStringWithErrorListener> = {
-  '0.13': compileString,
+  '0.14': compileString,
   '0.12': compileStringV012,
 };
 
diff --git a/src/editor/cashscript/version.ts b/src/editor/cashscript/version.ts
index 22c23b4..e5a1085 100644
--- a/src/editor/cashscript/version.ts
+++ b/src/editor/cashscript/version.ts
@@ -7,9 +7,9 @@
 // versions, which avoids re-registering providers (Monaco can't cleanly
 // unregister them) while still gating version-specific language features.
 
-export type CashScriptVersion = '0.12' | '0.13';
+export type CashScriptVersion = '0.12' | '0.14';
 
-let currentVersion: CashScriptVersion = '0.13';
+let currentVersion: CashScriptVersion = '0.14';
 
 // Listeners notified when the selected version changes. Used by the highlighting
 // layer, which (unlike completions/hover) is registered statically and must be
diff --git a/yarn.lock b/yarn.lock
index 1c01f3c..12e28b7 100644
--- a/yarn.lock
+++ b/yarn.lock
@@ -77,10 +77,10 @@
   dependencies:
     "@bitauth/libauth" "^3.1.0-next.8"
 
-"@cashscript/utils@^0.13.1":
-  version "0.13.1"
-  resolved "https://registry.yarnpkg.com/@cashscript/utils/-/utils-0.13.1.tgz#cfcfcf7c6a8edb41f4c3887b908592147c9a3736"
-  integrity sha512-MAZ0SK+wvgQbTKHHgTDocfOI+Yrmw5c8bv4FyKUuCtjw/+JE/HJEEKyL/0ppEFbOzv5Jy4JQIV6n7GPNWm/wbQ==
+"@cashscript/utils@^0.14.0-next.1":
+  version "0.14.0-next.1"
+  resolved "https://registry.yarnpkg.com/@cashscript/utils/-/utils-0.14.0-next.1.tgz#59b90cd817d72687c61ecbd5dcc535cb23021489"
+  integrity sha512-/xXCjcBCk5QDpUXiYwZ4fFxyzzW9PdkgVOGGWfYr3e/8ebtIQWQ+nlykqtre7h4cIbriDp3TXCHLoPHGiEwWVw==
   dependencies:
     "@bitauth/libauth" "^3.1.0-next.8"
 
@@ -1200,24 +1200,24 @@ caniuse-lite@^1.0.30001579:
     commander "^14.0.0"
     semver "^7.7.2"
 
-cashc@^0.13.1:
-  version "0.13.1"
-  resolved "https://registry.yarnpkg.com/cashc/-/cashc-0.13.1.tgz#9b246f2997eda2fbe5c358fdedbb36bdc57b5a96"
-  integrity sha512-u0tcMNyK29FOLhVzoQsynmd51QtAGxPIpy8pScLu18RV1MMI0WD1YJY1DBtRNaQlOupeBeO24O6lTNoJ621d2w==
+cashc@^0.14.0-next.1:
+  version "0.14.0-next.1"
+  resolved "https://registry.yarnpkg.com/cashc/-/cashc-0.14.0-next.1.tgz#17c0302e3343e06869e72527819666a15509359b"
+  integrity sha512-/sY7MLVDX6DoeqhWjv70YZOd5QDurTtPItI5k0NrhF7OMtS4do+hFBTrsgOB3FDF8mcUWAW/+jYnvrFbhoSQtg==
   dependencies:
     "@bitauth/libauth" "^3.1.0-next.8"
-    "@cashscript/utils" "^0.13.1"
+    "@cashscript/utils" "^0.14.0-next.1"
     antlr4 "^4.13.2"
     commander "^14.0.0"
     semver "^7.7.2"
 
-cashscript@^0.13.1:
-  version "0.13.1"
-  resolved "https://registry.yarnpkg.com/cashscript/-/cashscript-0.13.1.tgz#06059881922c35064347e13d97eeb0eb057eea3f"
-  integrity sha512-BrPFO4TYFTFc41Ft4Hpsky9UNct2SEv6QdC89utu4B/9+8kl4uJLy4SjUv9ZJciGSigQOg4McKYzuYCc/oYl2g==
+cashscript@^0.14.0-next.1:
+  version "0.14.0-next.1"
+  resolved "https://registry.yarnpkg.com/cashscript/-/cashscript-0.14.0-next.1.tgz#994ae26b9da916d918c48c4e3242526f10169c58"
+  integrity sha512-e3WD/rqH7y3+pIU827/n8aDdofWLveal844aSdMhe6/kTm1UHDcYNojZ6nYV4ncBx8zLb19xwx8UW/UaLXhvcw==
   dependencies:
     "@bitauth/libauth" "^3.1.0-next.8"
-    "@cashscript/utils" "^0.13.1"
+    "@cashscript/utils" "^0.14.0-next.1"
     "@electrum-cash/network" "^4.1.3"
     fflate "^0.8.2"
     semver "^7.7.2"