Merge field for Total Amount of Invoice

[Gears]

Below is how my Payment Reminders are setup:

 

Invoice #: {$invoice_num}

Invoice Total: {$invoice_total}

Remaining Balance: {$invoice_balance}

 

 

 

the $invoice_total field takes into account for credit that is applied. So for example if the invoice was for $500 and there was a $100 credit applied, the $invoice_total would display $400.

 

What merge field would I use to display the total, final amount of the invoice prior to credit being applied? $sub_total perhaps? But does that take into account tax?

 

I want something like this:

 

Invoice Total: $500

Credit Applied: $100

Remaining Balance: $400

 

Thank you