The balance remaining in a retainer account is the value of the Retainer Amount field in the retainer Billing Item (as created here), minus all payments from the account and plus all refunds to the account. A payment from a retainer account is created using a "Payment from Retainer" type Billing Item. A refund is created using a "Retainer Refund" type billing item.

There are two ways to view the balance in a retainer.

1. Add the RetainerBalance column to the Billing Items table:

2. Open the retainer Billing Item, where you will also see all payments from that retainer: