diff --git a/modules/ecash-coinselect/README.md b/modules/ecash-coinselect/README.md
--- a/modules/ecash-coinselect/README.md
+++ b/modules/ecash-coinselect/README.md
@@ -49,4 +49,8 @@
 
 -   Support input param `tokenInputs` to create txs with user-specified inputs [diff](https://reviews.bitcoinabc.org/D15520)
 
+2.1.0
+
+-   Export new function `getMaxSendAmountSatoshis` [diff](https://reviews.bitcoinabc.org/D15555)
+
 ## License [MIT](LICENSE)
diff --git a/modules/ecash-coinselect/index.js b/modules/ecash-coinselect/index.js
--- a/modules/ecash-coinselect/index.js
+++ b/modules/ecash-coinselect/index.js
@@ -3,5 +3,5 @@
 // Distributed under the MIT software license, see the accompanying
 // file LICENSE or http://www.opensource.org/licenses/mit-license.php.
 'use strict';
-const { coinSelect } = require('./src/coinSelect');
-module.exports = { coinSelect };
+const { coinSelect, getMaxSendAmountSatoshis } = require('./src/coinSelect');
+module.exports = { coinSelect, getMaxSendAmountSatoshis };
diff --git a/modules/ecash-coinselect/package.json b/modules/ecash-coinselect/package.json
--- a/modules/ecash-coinselect/package.json
+++ b/modules/ecash-coinselect/package.json
@@ -1,6 +1,6 @@
 {
     "name": "ecash-coinselect",
-    "version": "2.1.0",
+    "version": "2.2.0",
     "description": "An unspent transaction output (UTXO) selection module for eCash.",
     "main": "src/utxo.js",
     "scripts": {
diff --git a/modules/ecash-coinselect/src/coinSelect.js b/modules/ecash-coinselect/src/coinSelect.js
--- a/modules/ecash-coinselect/src/coinSelect.js
+++ b/modules/ecash-coinselect/src/coinSelect.js
@@ -94,4 +94,46 @@
     throw new Error('Insufficient funds');
 }
 
-module.exports = { coinSelect };
+/**
+ * Get the send amount for a 'send all' tx based on the utxos in a wallet
+ * Note: this function ignores token utxos from NNG chronik-client and in-node chronik-client
+ *
+ * @param {array} utxos [...{value: <valueAsString | valueAsNumber>}]
+ * @param {number} txFee fee in satoshis per byte (may have decimals e.g. 1.01)
+ * @param {array} otherTargetOutputs [...{address: <address>, value: <valueAsNumber}] targetOutputs
+ * in addition to the expected output of the wallet's max send amount
+ * e.g., if a user is sending max amount from Cashtab and also a Cashtab Msg, would be [{value: 0, script}]
+ * @returns {integer} max amount of satoshis the wallet can send (should leave a zero-balance, only token
+ * dust would be expected to remain in the wallet)
+ */
+const getMaxSendAmountSatoshis = (utxos, txFee, otherTargetOutputs = []) => {
+    // Ignore token utxos
+    const nonTokenUtxos = utxos.filter(utxo => !isToken(utxo));
+
+    // Get total send qty of all non-token
+    let totalSatsInWallet = nonTokenUtxos.reduce(
+        (previousBalance, utxo) => previousBalance + parseInt(utxo.value),
+        0,
+    );
+
+    // Get the bytecount of a tx that spends all the non-token utxos
+    const byteCount = transactionBytes(
+        nonTokenUtxos,
+        [{ value: totalSatsInWallet }].concat(otherTargetOutputs),
+    );
+
+    // Your final send amount should be totalSatsInWallet - (txFee in sats/byte)*(bytes of tx)
+    // We apply Math.ceil to (txFee * byteCount) so we get an integer.
+    const maxSendAmountSatoshis =
+        totalSatsInWallet - Math.ceil(txFee * byteCount);
+
+    // Test if this is a sendable output
+    if (maxSendAmountSatoshis < DUST_SATOSHIS) {
+        throw new Error(
+            `Insufficient funds to send any satoshis from this wallet at fee rate of ${txFee} satoshis per byte`,
+        );
+    }
+    return maxSendAmountSatoshis;
+};
+
+module.exports = { coinSelect, getMaxSendAmountSatoshis };
diff --git a/modules/ecash-coinselect/test/coinSelect.test.js b/modules/ecash-coinselect/test/coinSelect.test.js
--- a/modules/ecash-coinselect/test/coinSelect.test.js
+++ b/modules/ecash-coinselect/test/coinSelect.test.js
@@ -4,7 +4,7 @@
 // file LICENSE or http://www.opensource.org/licenses/mit-license.php.
 'use strict';
 const assert = require('assert');
-const { coinSelect } = require('../src/coinSelect');
+const { coinSelect, getMaxSendAmountSatoshis } = require('../src/coinSelect');
 
 const MOCK_TOKEN_UTXO = { value: '546' };
 const MOCK_TOKEN_SEND_OUTPUT = {
@@ -14,6 +14,8 @@
         'hex',
     ),
 };
+const OP_RETURN_MAX_SIZE =
+    '6a04007461624cd75f5f5f5f5f5f5f5f31305f5f5f5f5f5f5f5f31305f5f5f5f5f5f5f5f31305f5f5f5f5f5f5f5f31305f5f5f5f5f5f5f5f31305f5f5f5f5f5f5f5f31305f5f5f5f5f5f5f5f31305f5f5f5f5f5f5f5f31305f5f5f5f5f5f5f5f31305f5f5f5f5f5f5f5f31305f5f5f5f5f5f5f5f31305f5f5f5f5f5f5f5f31305f5f5f5f5f5f5f5f31305f5f5f5f5f5f5f5f31305f5f5f5f5f5f5f5f31305f5f5f5f5f5f5f5f31305f5f5f5f5f5f5f5f31305f5f5f5f5f5f5f5f31305f5f5f5f5f5f5f5f31305f5f5f5f5f5f5f5f31305f5f5f5f5f5f5f5f31305f5f323135';
 
 describe('coinSelect() accumulative algorithm for utxo selection in coinselect.js', async function () {
     it('adds a change output if change > dust', function () {
@@ -407,4 +409,78 @@
             coinSelect(stubChronikUtxos, [{ value: 900 }], 1);
         }, Error('Insufficient funds'));
     });
+    it('getMaxSendAmountSatoshis gets max send amount for a wallet with multiple utxos', function () {
+        const stubChronikUtxos = [
+            { value: '1000' },
+            { value: '2000' },
+            { value: '3000' },
+        ];
+        assert.equal(getMaxSendAmountSatoshis(stubChronikUtxos, 1), 5512);
+    });
+    it('getMaxSendAmountSatoshis gets the same result even if the wallet has token utxos with spendable amounts', function () {
+        const stubChronikUtxos = [
+            { value: '10000', token: {} }, // in-node chronik
+            { value: '10000', slpToken: {} }, // NNG chronik
+            { value: '1000' },
+            { value: '2000' },
+            { value: '3000' },
+        ];
+        assert.equal(getMaxSendAmountSatoshis(stubChronikUtxos, 1), 5512);
+    });
+    it('getMaxSendAmountSatoshis gets max send amount for a wallet with one utxo', function () {
+        const stubChronikUtxos = [{ value: '1000' }];
+        assert.equal(getMaxSendAmountSatoshis(stubChronikUtxos, 1), 808);
+    });
+    it('getMaxSendAmountSatoshis gets max send amount for a wallet with multiple utxos if the user specifies an OP_RETURN output', function () {
+        const stubChronikUtxos = [
+            { value: '1000' },
+            { value: '2000' },
+            { value: '3000' },
+        ];
+        assert.equal(
+            getMaxSendAmountSatoshis(stubChronikUtxos, 1, [
+                {
+                    value: 0,
+                    script: Buffer.from(OP_RETURN_MAX_SIZE, 'hex'),
+                },
+            ]),
+            5280,
+        );
+    });
+    it('getMaxSendAmountSatoshis gets max send amount for a wallet with multiple utxos at an arbitrary fee', function () {
+        const stubChronikUtxos = [
+            { value: '1000' },
+            { value: '2000' },
+            { value: '3000' },
+        ];
+        assert.equal(getMaxSendAmountSatoshis(stubChronikUtxos, 5.01), 3555);
+    });
+    it('getMaxSendAmountSatoshis throws error if wallet has insufficient funds to send a tx with the requested inputs and outputs', function () {
+        const stubChronikUtxos = [
+            { value: '1000' },
+            { value: '2000' },
+            { value: '3000' },
+        ];
+        assert.throws(() => {
+            getMaxSendAmountSatoshis(stubChronikUtxos, 17.01);
+        }, Error('Insufficient funds to send any satoshis from this wallet at fee rate of 17.01 satoshis per byte'));
+    });
+    it('getMaxSendAmountSatoshis will return dust amount if that is the max sendable amount', function () {
+        const stubChronikUtxos = [
+            { value: '1000' },
+            { value: '2000' },
+            { value: '3000' },
+        ];
+        assert.equal(getMaxSendAmountSatoshis(stubChronikUtxos, 11.176), 546);
+    });
+    it('getMaxSendAmountSatoshis will throw error if amount is 1 sat lower than dust', function () {
+        const stubChronikUtxos = [
+            { value: '1000' },
+            { value: '2000' },
+            { value: '3000' },
+        ];
+        assert.throws(() => {
+            getMaxSendAmountSatoshis(stubChronikUtxos, 11.177);
+        }, Error('Insufficient funds to send any satoshis from this wallet at fee rate of 11.177 satoshis per byte'));
+    });
 });