diff --git a/packages/extension/package.json b/packages/extension/package.json
index 6a0999c11..0097877db 100644
--- a/packages/extension/package.json
+++ b/packages/extension/package.json
@@ -24,6 +24,7 @@
   },
   "dependencies": {
     "@amplitude/analytics-browser": "^2.42.4",
+    "@bitcoinerlab/secp256k1": "^1.2.0",
     "@enkryptcom/extension-bridge": "workspace:^",
     "@enkryptcom/hw-wallets": "workspace:^",
     "@enkryptcom/keyring": "workspace:^",
diff --git a/packages/extension/src/providers/bitcoin/libs/init-ecc.ts b/packages/extension/src/providers/bitcoin/libs/init-ecc.ts
new file mode 100644
index 000000000..29f25d110
--- /dev/null
+++ b/packages/extension/src/providers/bitcoin/libs/init-ecc.ts
@@ -0,0 +1,13 @@
+import * as ecc from '@bitcoinerlab/secp256k1';
+import { initEccLib } from 'bitcoinjs-lib';
+
+/**
+ * bitcoinjs-lib does not bundle an elliptic curve implementation. Anything
+ * taproot related throws `No ECC Library provided` until one is registered,
+ * which makes `address.toOutputScript` reject every `bc1p...` address and, in
+ * turn, makes taproot recipients look invalid and unspendable to.
+ *
+ * Importing this module for its side effect registers the curve once. Import it
+ * from any module that validates addresses or builds output scripts.
+ */
+initEccLib(ecc);
diff --git a/packages/extension/src/providers/bitcoin/libs/utils.ts b/packages/extension/src/providers/bitcoin/libs/utils.ts
index 6da7331ca..bca9d4792 100644
--- a/packages/extension/src/providers/bitcoin/libs/utils.ts
+++ b/packages/extension/src/providers/bitcoin/libs/utils.ts
@@ -1,3 +1,4 @@
+import './init-ecc';
 import { BitcoinNetworkInfo, HaskoinUnspentType } from '../types';
 import { address as BTCAddress } from 'bitcoinjs-lib';
 import { GasPriceTypes } from '@/providers/common/types';
diff --git a/packages/extension/src/providers/bitcoin/tests/bitcoin.address.validation.test.ts b/packages/extension/src/providers/bitcoin/tests/bitcoin.address.validation.test.ts
new file mode 100644
index 000000000..16e47073b
--- /dev/null
+++ b/packages/extension/src/providers/bitcoin/tests/bitcoin.address.validation.test.ts
@@ -0,0 +1,89 @@
+// @vitest-environment node
+//
+// bitcoinjs-lib verifies an ECC library by feeding it `Buffer.from(...)` test
+// vectors, and @noble/curves rejects anything that is not a `Uint8Array`. Under
+// the default jsdom environment those two come from different realms, so the
+// `instanceof` check fails and `initEccLib` throws even though the library is
+// fine. In a browser there is a single realm and the bundled Buffer polyfill
+// extends that realm's Uint8Array, so this only affects the test harness.
+import { describe, it, expect } from 'vitest';
+import bitcoinNetworks from '../networks';
+import { isAddress } from '../libs/utils';
+import {
+  calculateSizeBasedOnType,
+  getOutputCounterForAddress,
+} from '../ui/libs/tx-size';
+import { PaymentType } from '../types/bitcoin-network';
+
+const bitcoin = bitcoinNetworks.bitcoin.networkInfo;
+const litecoin = bitcoinNetworks.litecoin.networkInfo;
+
+// BIP86 test vector
+const TAPROOT =
+  'bc1p5cyxnuxmeuwuvkwfem96lqzszd02n6xdcjrs20cac6yqjjwudpxqkedrcr';
+const NATIVE_SEGWIT = 'bc1qw508d6qejxtdg4y5r3zarvary0c5xw7kv8f3t4';
+const P2SH = '3J98t1WpEZ73CNmQviecrnyiWrnqRhWNLy';
+const P2PKH = '1BvBMSEYstWetqTFn5Au4m4GFg7xJaNVN2';
+const P2WSH = 'bc1qrp33g0q5c5txsp9arysrx4k6zdkfs4nce4xj0gdcccefvpysxf3qccfmv3';
+
+describe('Should validate bitcoin recipient addresses', () => {
+  it('should accept taproot addresses', () => {
+    expect(isAddress(TAPROOT, bitcoin)).to.be.eq(true);
+  });
+
+  it('should accept every other standard mainnet address type', () => {
+    expect(isAddress(NATIVE_SEGWIT, bitcoin)).to.be.eq(true);
+    expect(isAddress(P2WSH, bitcoin)).to.be.eq(true);
+    expect(isAddress(P2SH, bitcoin)).to.be.eq(true);
+    expect(isAddress(P2PKH, bitcoin)).to.be.eq(true);
+  });
+
+  it('should reject malformed addresses and addresses from another network', () => {
+    expect(isAddress('not an address', bitcoin)).to.be.eq(false);
+    expect(isAddress('', bitcoin)).to.be.eq(false);
+    // valid taproot address, wrong network
+    expect(isAddress(TAPROOT, litecoin)).to.be.eq(false);
+    // checksum broken on the last character
+    expect(isAddress(`${TAPROOT.slice(0, -1)}p`, bitcoin)).to.be.eq(false);
+  });
+});
+
+describe('Should size outputs by their address type', () => {
+  it('should classify bech32 and bech32m outputs', () => {
+    expect(getOutputCounterForAddress(TAPROOT)).to.be.eq('p2tr_output_count');
+    expect(getOutputCounterForAddress(NATIVE_SEGWIT)).to.be.eq(
+      'p2wpkh_output_count',
+    );
+    expect(getOutputCounterForAddress(P2WSH)).to.be.eq('p2wsh_output_count');
+  });
+
+  it('should fall back to the account type for anything else', () => {
+    expect(getOutputCounterForAddress(P2SH)).to.be.eq(undefined);
+    expect(getOutputCounterForAddress(P2PKH)).to.be.eq(undefined);
+    expect(getOutputCounterForAddress('')).to.be.eq(undefined);
+  });
+
+  it('should charge for the larger taproot output', () => {
+    const toSegwit = calculateSizeBasedOnType(1, 2, PaymentType.P2WPKH, [
+      NATIVE_SEGWIT,
+    ]);
+    const toTaproot = calculateSizeBasedOnType(1, 2, PaymentType.P2WPKH, [
+      TAPROOT,
+    ]);
+    // P2TR_OUT_SIZE (43) - P2WPKH_OUT_SIZE (31)
+    expect(toTaproot - toSegwit).to.be.eq(12);
+  });
+
+  it('should size unknown outputs as the account type, as before', () => {
+    const withoutAddresses = calculateSizeBasedOnType(1, 2, PaymentType.P2WPKH);
+    expect(
+      calculateSizeBasedOnType(1, 2, PaymentType.P2WPKH, [NATIVE_SEGWIT]),
+    ).to.be.eq(withoutAddresses);
+    expect(calculateSizeBasedOnType(1, 2, PaymentType.P2WPKH, [''])).to.be.eq(
+      withoutAddresses,
+    );
+    expect(calculateSizeBasedOnType(1, 2, PaymentType.P2WPKH, [P2SH])).to.be.eq(
+      withoutAddresses,
+    );
+  });
+});
diff --git a/packages/extension/src/providers/bitcoin/ui/libs/signer.ts b/packages/extension/src/providers/bitcoin/ui/libs/signer.ts
index 27f85e6fa..c226688d8 100644
--- a/packages/extension/src/providers/bitcoin/ui/libs/signer.ts
+++ b/packages/extension/src/providers/bitcoin/ui/libs/signer.ts
@@ -1,3 +1,4 @@
+import '../../libs/init-ecc';
 import { InternalMethods, InternalOnMessageResponse } from '@/types/messenger';
 import { SignerTransactionOptions, SignerMessageOptions } from '../types';
 import sendUsingInternalMessengers from '@/libs/messenger/internal-messenger';
diff --git a/packages/extension/src/providers/bitcoin/ui/libs/tx-size.ts b/packages/extension/src/providers/bitcoin/ui/libs/tx-size.ts
index 1cfa48830..40184a692 100644
--- a/packages/extension/src/providers/bitcoin/ui/libs/tx-size.ts
+++ b/packages/extension/src/providers/bitcoin/ui/libs/tx-size.ts
@@ -1,6 +1,7 @@
 // https://github.com/jlopp/bitcoin-transaction-size-calculator/blob/master/index.html
 
 import { toBN } from 'web3-utils';
+import { address as BTCAddress } from 'bitcoinjs-lib';
 import { PaymentType } from '../../types/bitcoin-network';
 
 enum InputScriptType {
@@ -234,16 +235,52 @@ const calculateSize = (
     txWeight,
   };
 };
+/**
+ * Bucket an output address into the counter `calculateSize` uses for it.
+ *
+ * Only bech32/bech32m outputs are classified. Those are the ones whose size
+ * differs enough from the account's own output type to matter: a P2TR or P2WSH
+ * output is 43 vB against 31 vB for P2WPKH, which is the difference between a
+ * transaction relaying and being dropped for paying under the minimum fee rate.
+ * Anything else falls back to the account's own type, which is at most 3 vB out.
+ */
+const getOutputCounterForAddress = (
+  address: string,
+): keyof calcOutputType | undefined => {
+  let decoded: { version: number; data: Buffer };
+  try {
+    decoded = BTCAddress.fromBech32(address);
+  } catch {
+    return undefined;
+  }
+  if (decoded.version === 0) {
+    if (decoded.data.length === 20) return 'p2wpkh_output_count';
+    if (decoded.data.length === 32) return 'p2wsh_output_count';
+  } else if (decoded.version === 1 && decoded.data.length === 32) {
+    return 'p2tr_output_count';
+  }
+  return undefined;
+};
+
+/**
+ * `outputAddresses` describes the outputs that are already known, in order. Any
+ * output without a matching entry — the change output, or a recipient address
+ * that is still being typed — is sized as the account's own payment type.
+ */
 const calculateSizeBasedOnType = (
   numInputs: number,
   numOutputs: number,
   type: PaymentType,
+  outputAddresses: string[] = [],
 ): number => {
+  const defaultCounter: keyof calcOutputType =
+    type === PaymentType.P2PKH ? 'p2pkh_output_count' : 'p2wpkh_output_count';
   const output: calcOutputType = {};
-  if (type === PaymentType.P2PKH) {
-    output.p2pkh_output_count = numOutputs;
-  } else {
-    output.p2wpkh_output_count = numOutputs;
+  for (let i = 0; i < numOutputs; i++) {
+    const counter =
+      (outputAddresses[i] && getOutputCounterForAddress(outputAddresses[i])) ||
+      defaultCounter;
+    output[counter] = (output[counter] ?? 0) + 1;
   }
   const size = calculateSize(
     {
@@ -257,4 +294,9 @@ const calculateSizeBasedOnType = (
   );
   return type === PaymentType.P2PKH ? size.txBytes : size.txVBytes;
 };
-export { InputScriptType, calculateSize, calculateSizeBasedOnType };
+export {
+  InputScriptType,
+  calculateSize,
+  calculateSizeBasedOnType,
+  getOutputCounterForAddress,
+};
diff --git a/packages/extension/src/providers/bitcoin/ui/send-transaction/index.vue b/packages/extension/src/providers/bitcoin/ui/send-transaction/index.vue
index 8937fe6fc..e164d932d 100644
--- a/packages/extension/src/providers/bitcoin/ui/send-transaction/index.vue
+++ b/packages/extension/src/providers/bitcoin/ui/send-transaction/index.vue
@@ -279,7 +279,7 @@ const nativeBalanceAfterTransaction = computed(() => {
 
 const setTransactionFees = (byteSize: number) => {
   const nativeVal = selectedAsset.value.price || '0';
-  getGasCostValues(
+  return getGasCostValues(
     props.network as BitcoinNetwork,
     byteSize,
     nativeVal,
@@ -294,16 +294,26 @@ const setBaseCosts = () => {
   });
 };
 
+/**
+ * The recipient output is sized from `addressTo` so that sending to an address
+ * type larger than our own — a taproot one, say — is not underpaid. The change
+ * output has no entry and is sized as our own payment type.
+ */
+const updateTransactionFees = () => {
+  const txSize = calculateSizeBasedOnType(
+    accountUTXOs.value.length + (isSendToken.value ? 0 : 1),
+    2,
+    (props.network as BitcoinNetwork).networkInfo.paymentType,
+    [addressTo.value],
+  );
+  return setTransactionFees(Math.ceil(txSize));
+};
+
 const updateUTXOs = async () => {
   const api = (await props.network.api()) as BitcoinAPI;
   return api.getUTXOs(addressFrom.value).then(utxos => {
     accountUTXOs.value = utxos;
-    const txSize = calculateSizeBasedOnType(
-      accountUTXOs.value.length + (isSendToken.value ? 0 : 1),
-      2,
-      (props.network as BitcoinNetwork).networkInfo.paymentType,
-    );
-    setTransactionFees(Math.ceil(txSize));
+    return updateTransactionFees();
   });
 };
 
@@ -369,6 +379,12 @@ watch([addressFrom], () => {
   }
 });
 
+watch([addressTo], () => {
+  updateTransactionFees().then(() => {
+    if (isMaxSelected.value) setMaxValue();
+  });
+});
+
 const isOpenSelectContactFrom = ref<boolean>(false);
 const isOpenSelectContactTo = ref<boolean>(false);
 
diff --git a/packages/extension/src/ui/action/views/swap/libs/bitcoin-gasvals.ts b/packages/extension/src/ui/action/views/swap/libs/bitcoin-gasvals.ts
index d94afcd0e..1de50a829 100644
--- a/packages/extension/src/ui/action/views/swap/libs/bitcoin-gasvals.ts
+++ b/packages/extension/src/ui/action/views/swap/libs/bitcoin-gasvals.ts
@@ -15,6 +15,7 @@ export const getBitcoinGasVals = async (
     tx.inputs.length,
     2,
     (network as BitcoinNetwork).networkInfo.paymentType,
+    tx.outputs.map(output => output.address),
   );
   return getGasCostValues(
     network as BitcoinNetwork,
diff --git a/yarn.lock b/yarn.lock
index 5d47e4bb5..65d0c311d 100644
--- a/yarn.lock
+++ b/yarn.lock
@@ -1726,6 +1726,7 @@ __metadata:
   resolution: "@enkryptcom/extension@workspace:packages/extension"
   dependencies:
     "@amplitude/analytics-browser": "npm:^2.42.4"
+    "@bitcoinerlab/secp256k1": "npm:^1.2.0"
     "@crxjs/vite-plugin": "npm:^2.4.0"
     "@enkryptcom/extension-bridge": "workspace:^"
     "@enkryptcom/hw-wallets": "workspace:^"