Magento Open Source, 1.9.x
Partial Authorization with Authorize.Net

Authorize.Net gives you the ability to accept multiple credit cards as payment for a single order. If there isn’t enough remaining balance on a single card to cover the purchase, the amount can be distributed across multiple cards. Up to five credit cards can be used to pay for a single order. Partial authorization can be activated in the Authorize.Net configuration at either the global, or website level.

Partial Authorization During Checkout

To enable partial authorization:

1. On the Admin menu, select System > Configuration.
2. In the panel on the left under Sales, select Payment Methods. Then, click to expand the Authorize.Net section.
3. Set Allow Partial Authorization to “Yes.”
4. When complete, click the Save Config button.