How to add fee to order totals in Magento 2

follow below steps it will help you, in my module, I just added fee column
this will add one row in cart total called fee and also side bar in the checkout page
and also it added fee amount to total amount (fee static value I kept as 100) once the order is placed total will be with fee and if you are logged in fronted in order view you can see fee's new row in the total block but admin side not yet implemented if someone implements, you can post that answer

create sales.xml in your module etc folder

<?xml version="1.0"?>

<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:module:Magento_Sales:etc/sales.xsd">
    <section name="quote">
        <group name="totals">

            <item name="fee" instance="Sugarcode\Test\Model\Total\Fee" sort_order="150"/>

        </group>  
    </section>
</config>

app\code\Sugarcode\Test\view\frontend\web\js\view\checkout\cart\totals\fee.js

/**
 * Copyright © 2015 Magento. All rights reserved.
 * See COPYING.txt for license details.
 */
define(
    [
        'Sugarcode_Test/js/view/checkout/summary/fee'
    ],
    function (Component) {
        'use strict';

        return Component.extend({

            /**
             * @override
             */
            isDisplayed: function () {
                return true;
            }
        });
    }
);

app\code\Sugarcode\Test\view\frontend\web\js\view\checkout\summary\fee.js

/**
 * Copyright © 2015 Magento. All rights reserved.
 * See COPYING.txt for license details.
 */
/*jshint browser:true jquery:true*/
/*global alert*/
define(
    [
        'Magento_Checkout/js/view/summary/abstract-total',
        'Magento_Checkout/js/model/quote',
        'Magento_Catalog/js/price-utils',
        'Magento_Checkout/js/model/totals'
    ],
    function (Component, quote, priceUtils, totals) {
        "use strict";
        return Component.extend({
            defaults: {
                isFullTaxSummaryDisplayed: window.checkoutConfig.isFullTaxSummaryDisplayed || false,
                template: 'Sugarcode_Test/checkout/summary/fee'
            },
            totals: quote.getTotals(),
            isTaxDisplayedInGrandTotal: window.checkoutConfig.includeTaxInGrandTotal || false,
            isDisplayed: function() {
                return this.isFullMode();
            },
            getValue: function() {
                var price = 0;
                if (this.totals()) {
                    price = totals.getSegment('fee').value;
                }
                return this.getFormattedPrice(price);
            },
            getBaseValue: function() {
                var price = 0;
                if (this.totals()) {
                    price = this.totals().base_fee;
                }
                return priceUtils.formatPrice(price, quote.getBasePriceFormat());
            }
        });
    }
);

app\code\Sugarcode\Test\view\frontend\web\template\checkout\summary\fee.html

<!--
/**
 * Copyright © 2015 Magento. All rights reserved.
 * See COPYING.txt for license details.
 */
-->
<!-- ko -->

  <tr class="totals fee excl">
        <th class="mark" scope="row">
            <span class="label" data-bind="text: title"></span>
            <span class="value" data-bind="text: getValue()"></span>
        </th>
        <td class="amount">

            <span class="price"
                  data-bind="text: getValue(), attr: {'data-th': title}"></span>


        </td>
    </tr>   

<!-- /ko -->

app\code\Sugarcode\Test\view\frontend\web\template\checkout\cart\totals\fee.html

<!--
/**
 * Copyright © 2015 Magento. All rights reserved.
 * See COPYING.txt for license details.
 */
-->
<!-- ko -->
<tr class="totals fee excl">
    <th class="mark" colspan="1" scope="row" data-bind="text: title"></th>
    <td class="amount">
        <span class="price" data-bind="text: getValue()"></span>
    </td>
</tr>
<!-- /ko -->

app\code\Sugarcode\Test\Model\Total\Fee.php

<?php
/**
 * Copyright © 2015 Magento. All rights reserved.
 * See COPYING.txt for license details.
 */
namespace Sugarcode\Test\Model\Total;


class Fee extends \Magento\Quote\Model\Quote\Address\Total\AbstractTotal
{
   /**
     * Collect grand total address amount
     *
     * @param \Magento\Quote\Model\Quote $quote
     * @param \Magento\Quote\Api\Data\ShippingAssignmentInterface $shippingAssignment
     * @param \Magento\Quote\Model\Quote\Address\Total $total
     * @return $this
     */
    protected $quoteValidator = null; 

    public function __construct(\Magento\Quote\Model\QuoteValidator $quoteValidator)
    {
        $this->quoteValidator = $quoteValidator;
    }
  public function collect(
        \Magento\Quote\Model\Quote $quote,
        \Magento\Quote\Api\Data\ShippingAssignmentInterface $shippingAssignment,
        \Magento\Quote\Model\Quote\Address\Total $total
    ) {
        parent::collect($quote, $shippingAssignment, $total);


        $exist_amount = 0; //$quote->getFee(); 
        $fee = 100; //Excellence_Fee_Model_Fee::getFee();
        $balance = $fee - $exist_amount;

        $total->setTotalAmount('fee', $balance);
        $total->setBaseTotalAmount('fee', $balance);

        $total->setFee($balance);
        $total->setBaseFee($balance);

        $total->setGrandTotal($total->getGrandTotal() + $balance);
        $total->setBaseGrandTotal($total->getBaseGrandTotal() + $balance);


        return $this;
    } 

    protected function clearValues(Address\Total $total)
    {
        $total->setTotalAmount('subtotal', 0);
        $total->setBaseTotalAmount('subtotal', 0);
        $total->setTotalAmount('tax', 0);
        $total->setBaseTotalAmount('tax', 0);
        $total->setTotalAmount('discount_tax_compensation', 0);
        $total->setBaseTotalAmount('discount_tax_compensation', 0);
        $total->setTotalAmount('shipping_discount_tax_compensation', 0);
        $total->setBaseTotalAmount('shipping_discount_tax_compensation', 0);
        $total->setSubtotalInclTax(0);
        $total->setBaseSubtotalInclTax(0);
    }
    /**
     * @param \Magento\Quote\Model\Quote $quote
     * @param Address\Total $total
     * @return array|null
     */
    /**
     * Assign subtotal amount and label to address object
     *
     * @param \Magento\Quote\Model\Quote $quote
     * @param Address\Total $total
     * @return array
     * @SuppressWarnings(PHPMD.UnusedFormalParameter)
     */
    public function fetch(\Magento\Quote\Model\Quote $quote, \Magento\Quote\Model\Quote\Address\Total $total)
    {
        return [
            'code' => 'fee',
            'title' => 'Fee',
            'value' => 100
        ];
    }

    /**
     * Get Subtotal label
     *
     * @return \Magento\Framework\Phrase
     */
    public function getLabel()
    {
        return __('Fee');
    }
}

app\code\Sugarcode\Test\etc\module.xml

<?xml version="1.0"?>
<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="../../../../../lib/internal/Magento/Framework/Module/etc/module.xsd">
    <module name="Sugarcode_Test" setup_version="2.0.6" schema_version="2.0.6">
        <sequence>
            <module name="Magento_Sales"/>
            <module name="Magento_Quote"/>
            <module name="Magento_Checkout"/>
        </sequence>
    </module>
</config>

app\code\Sugarcode\Test\view\frontend\layout\checkout_cart_index.xml

<?xml version="1.0"?>
<!--
/**
 * Copyright © 2015 Magento. All rights reserved.
 * See COPYING.txt for license details.
 */
-->
<page xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:View/Layout/etc/page_configuration.xsd">
    <body>
        <referenceBlock name="checkout.cart.totals">
            <arguments>
                <argument name="jsLayout" xsi:type="array">
                    <item name="components" xsi:type="array">
                        <item name="block-totals" xsi:type="array">
                            <item name="children" xsi:type="array">


                                <item name="fee" xsi:type="array">
                                    <item name="component"  xsi:type="string">Sugarcode_Test/js/view/checkout/cart/totals/fee</item>
                                    <item name="sortOrder" xsi:type="string">20</item>
                                    <item name="config" xsi:type="array">
                                         <item name="template" xsi:type="string">Sugarcode_Test/checkout/cart/totals/fee</item>
                                        <item name="title" xsi:type="string" translate="true">Fee</item>
                                    </item>
                                </item>

                            </item>
                        </item>
                    </item>
                </argument>
            </arguments>
        </referenceBlock>
    </body>
</page>

app\code\Sugarcode\Test\view\frontend\layout\checkout_index_index.xml

<?xml version="1.0"?>
<!--
/**
 * Copyright © 2015 Magento. All rights reserved.
 * See COPYING.txt for license details.
 */
-->
<page xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" layout="1column" xsi:noNamespaceSchemaLocation="urn:magento:framework:View/Layout/etc/page_configuration.xsd">
    <body>
        <referenceBlock name="checkout.root">
            <arguments>
                <argument name="jsLayout" xsi:type="array">
                    <item name="components" xsi:type="array">
                        <item name="checkout" xsi:type="array">
                            <item name="children" xsi:type="array">

                                <item name="sidebar" xsi:type="array">
                                    <item name="children" xsi:type="array">
                                        <item name="summary" xsi:type="array">
                                            <item name="children" xsi:type="array">
                                                <item name="totals" xsi:type="array">
                                                    <item name="children" xsi:type="array">
                                                       <item name="fee" xsi:type="array">
                                                            <item name="component"  xsi:type="string">Sugarcode_Test/js/view/checkout/cart/totals/fee</item>
                                                            <item name="sortOrder" xsi:type="string">20</item>
                                                            <item name="config" xsi:type="array">
                                                                 <item name="template" xsi:type="string">Sugarcode_Test/checkout/cart/totals/fee</item>
                                                                <item name="title" xsi:type="string" translate="true">Fee</item>
                                                            </item>
                                                        </item>
                                                    </item>
                                                </item>
                                                <item name="cart_items" xsi:type="array">
                                                    <item name="children" xsi:type="array">
                                                        <item name="details" xsi:type="array">
                                                            <item name="children" xsi:type="array">
                                                                <item name="subtotal" xsi:type="array">
                                                                    <item name="component" xsi:type="string">Magento_Tax/js/view/checkout/summary/item/details/subtotal</item>
                                                                </item>
                                                            </item>
                                                        </item>
                                                    </item>
                                                </item>
                                            </item>
                                        </item>
                                    </item>
                                </item>
                            </item>
                        </item>
                    </item>
                </argument>
            </arguments>
        </referenceBlock>
    </body>
</page>

app\code\Sugarcode\Test\view\frontend\layout\sales_order_view.xml

<?xml version="1.0"?>
<!--
/**
 * Copyright © 2015 Magento. All rights reserved.
 * See COPYING.txt for license details.
 */
-->
<page xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:View/Layout/etc/page_configuration.xsd">

    <body>        
        <referenceContainer name="order_totals">
            <block class="Sugarcode\Test\Block\Sales\Order\Fee" name="fee"/>
        </referenceContainer>
    </body>
</page>

app\code\Sugarcode\Test\Block\Sales\Order\Fee.php

<?php
/**
 * Copyright © 2015 Magento. All rights reserved.
 * See COPYING.txt for license details.
 */

/**
 * Tax totals modification block. Can be used just as subblock of \Magento\Sales\Block\Order\Totals
 */
namespace Sugarcode\Test\Block\Sales\Order;



class Fee extends \Magento\Framework\View\Element\Template
{
    /**
     * Tax configuration model
     *
     * @var \Magento\Tax\Model\Config
     */
    protected $_config;

    /**
     * @var Order
     */
    protected $_order;

    /**
     * @var \Magento\Framework\DataObject
     */
    protected $_source;

    /**
     * @param \Magento\Framework\View\Element\Template\Context $context
     * @param \Magento\Tax\Model\Config $taxConfig
     * @param array $data
     */
    public function __construct(
        \Magento\Framework\View\Element\Template\Context $context,
        \Magento\Tax\Model\Config $taxConfig,
        array $data = []
    ) {
        $this->_config = $taxConfig;
        parent::__construct($context, $data);
    }

    /**
     * Check if we nedd display full tax total info
     *
     * @return bool
     */
    public function displayFullSummary()
    {
        return true;
    }

    /**
     * Get data (totals) source model
     *
     * @return \Magento\Framework\DataObject
     */
    public function getSource()
    {
        return $this->_source;
    } 
    public function getStore()
    {
        return $this->_order->getStore();
    }

      /**
     * @return Order
     */
    public function getOrder()
    {
        return $this->_order;
    }

    /**
     * @return array
     */
    public function getLabelProperties()
    {
        return $this->getParentBlock()->getLabelProperties();
    }

    /**
     * @return array
     */
    public function getValueProperties()
    {
        return $this->getParentBlock()->getValueProperties();
    }

    /**
     * Initialize all order totals relates with tax
     *
     * @return \Magento\Tax\Block\Sales\Order\Tax
     */
     public function initTotals()
    {

        $parent = $this->getParentBlock();
        $this->_order = $parent->getOrder();
        $this->_source = $parent->getSource();

        $store = $this->getStore();

        $fee = new \Magento\Framework\DataObject(
                [
                    'code' => 'fee',
                    'strong' => false,
                    'value' => 100,
                    //'value' => $this->_source->getFee(),
                    'label' => __('Fee'),
                ]
            );

            $parent->addTotal($fee, 'fee');
           // $this->_addTax('grand_total');
            $parent->addTotal($fee, 'fee');


            return $this;
    }

}

once the above steps are done run below command this is important else your js & Html files will be missing from pub/static folder. So run below command which will create js and html file in pub/static folder

bin\magento setup:static-content:deploy  

if works accept my answer which helps others


The answer of Pradeep is very helpful, but misses an important point.

The function Sugarcode\Test\Model\Total::collect() is called twice by Magento's Magento\Quote\Model\QuoteTotalsCollector::collect(), once for each address. At that point it creates a combined total that is stored in the quote table. It does not show up in the order, nor on the website in the checkout.

For this reason it is important to collect the fee in only one of times that collect() is called. This can be done by checking if there are any shipped items available:

    $items = $shippingAssignment->getItems();
    if (!count($items)) {
        return $this;
    }

Add this code at the beginning of your variant of Sugarcode\Test\Model\Total::collect()


please comment

        $total->setGrandTotal($total->getGrandTotal() + $balance);

form app\code\Sugarcode\Test\Model\Total\Fee.php for double custom fee issue

Hope it will help you!!