If your business sells into more than one state, each state where you have nexus taxes only its share of your income. That share is set by apportionment. Georgia, like most states now, uses a single sales factor, so your percentage depends entirely on where your sales happened.
The hard part is deciding where a service sale happened. Cost of performance sources it to wherever the work was done. Market-based sourcing sources it to wherever the customer received the benefit. Georgia uses market-based sourcing. For a Georgia consulting firm with clients in ten states, that difference decides whether nearly all of its income stays in Georgia or follows the clients.
Georgia also has no throwback rule, so a sale into a state where you have no nexus doesn't get pulled back into Georgia's tax base. That can help a business that sells out of state. It can also leave some income taxed nowhere, which is worth raising with a CPA rather than assuming it will sort itself out.
Online sellers have another layer to watch. Inventory sitting in an out-of-state fulfillment center, or crossing a state's economic threshold, can create income tax nexus somewhere you never planned to file.
The full article includes a worked example with a Georgia marketing agency and a short list of questions to answer before expanding across state lines. Read the full article on the Fusion CPA blog