Are you planning to publish in an open access journal?
Most require that you pay an APC.
Are you planning to publish in a journal covered by a UMBC Open Access Agreement?
If so, if you're the corresponding author, the Library has already paid for OA for your article, so you won't have to pay a fee.
Does your funding agency have an agreement with your publisher?
Some publishers and funders have agreements that will allow for OA without you paying a fee. Further, many publisher's will deposit your work in funders' required repositories for you. Other publishers will require you to pay an OA fee. Check your publisher's website to find out.
Is your work covered by the UMBC Open Access Policy (this policy is in the works but not yet in place)?
If the publisher’s embargo period conflicts with the funder’s OA requirement, the UMBC OA Policy for Employees overrides publisher’s requirements, so if your work is covered by it, paying an APC isn’t necessary. However, some publishers will only publish your work if you obtain a waiver to the policy, in which case you’ll have to pay the APC. If you’re affiliated with UMBC but not an employee, you can also opt to have your works covered by the policy by signing an Individual Open Access License to avoid paying OA APCs for immediate OA. Again, if your publisher requires you obtain a waiver to the policy, you’ll have to pay the APC.