Hi Kalyan - thank you for reaching out.
Meter readings are taken regularly every three months, and at move-in/move-out, unless there is an access issue.
If you are receiving monthly billing, this means that 2 bills out of three will be based on an estimate, with the third being a catch-up, either higher or lower depending on whether usage had been under or over estimated.
If you would prefer to only receive bills based on actual reads, you can adjust your billing frequency to quarterly, either on the AGL app or via MyAccount (at agl.com.au) so your invoices are only issued once the quarterly read has been taken.
Kind regards,
Xander