For 1099 contractors & freelancers
Yes, fees on business accounts and payment processors like Stripe, PayPal, and Square are deductible.
Schedule C, line 10 (Commissions and fees) or line 27a (Other expenses).
Processing fees taken out of client payments are a real business cost. Report the gross payment as income and deduct the fee, so your income matches the 1099-K.
Monthly fees, wire fees, and overdraft fees on a personal account are personal, which is one reason a separate business account helps.
Processor statements and bank statements.
In Smart Deductions, this is suggested as Bank & Payment Fees (Schedule C line 27a). You confirm it before it counts.
Sources
General information, not tax advice. For your specific situation, check with a CPA or Enrolled Agent.