The expiry date is calculated from the date you apply it. It doesn't "stack" or "extend" existing recharges, and you will be losing your balance of current plan.
Also note, most of the current promotions are for new customer sim packs (value is loaded onto the sim itself), and are not for existing customer recharge purposes.There has been some recharge promotions through retailers in the past, but none for a few months now unfortunately.
* I am a Boost Australia customer. This is a peer to peer community where users help each other.
