An accountable plan is an IRS-approved reimbursement policy that lets an S-corp pay its owner-employees back for legitimate business expenses (home office, cell phone, mileage, internet, etc.) tax-free to the owner and fully deductible to the business. Without one, those out-of-pocket expenses became non-deductible after the Tax Cuts and Jobs Act suspended misc itemized deductions. The plan is one of the simplest tax structures to set up: a written policy, monthly expense reports, and a return-of-excess rule. Most S-corp owners never set one up because it's a documentation system, not a return line item, and most tax preparers don't proactively recommend it.