Magento 1.7 Admin URL – How to Get Admin Page URL

If the url is determined by a controller and an action you can use this:

{{store url="module/controller/action"}}

If the url is to a cms page you this:

{{store _direct="url-key-here"}}

if you want some query params also like /some-ulr?a=2&b=5 use one of the methods above and add a _query parameter.

{{store url="module/controller/action" _query="a=2&b=5"}}
{{store _direct="url-key-here" _query="a=2&b=5"}}

[EDIT]
You can get the same urls in a template file like this:

$this->getUrl('module/controller/action'); //for controller pages
$this->getUrl('', array('_direct'=>'some-url-key')); //for cms pages
$this->getUrl('module/controller/action', array('_query'=>'a=2&b=5')); //for query params
$this->getUrl('', array('_direct'=>'some-url-key', '_query'=>'a=2&b=5')); //for query params

If want to get admin URL to Magento 2 then your can try below Solution

In order to get admin URL ,you need to inject the Magento_Backend ‘s helper class Magento\Backend\Helper\Data to __construct() function.

/**
 * @var Magento\Backend\Helper\Data
 */
protected $HelperBackend;

public function __construct(
.....
\Magento\Backend\Helper\Data $HelperBackend
....
) {
$this->HelperBackend = $HelperBackend;
}

/**
 *
 * @param \Magento\Framework\Event\Observer $observer
 * @return void
 */
public function getAdminUrl()
{
echo $this->HelperBackend->getHomePageUrl();
}