How to get backend Url in Magento 2?

It’s quite easy to fetch Base URL for an Admin panel/Backend in Magento 2 using Backend module Url Class.

Back end Url have base store Url plus admin URI name. like {BASE_URL}/admin/

You can get Magento2 backend URL by just below way,

public function __construct(
    \Magento\Backend\Model\Url $backendUrlManager
) {
    $this->backendUrlManager  = $backendUrlManager;
}

public function getBackendUrl()
{
    return $this->backendUrlManager->getUrl('sales/order/view', ['param1' => 'param1']);
}

We have passed Sales/order/view action with a query string as param1 in URL.

Get URL from an adminhtml template or PHP file,
echo $this->getBackendUrl();