Our problem with sending estimates by check: Virginia no longer accepts checks over $1500 per quarter, mandating electronic payments on its website that's not user-friendly. New York's Dept of Revenue online somehow does not "recognize" the (correct) taxpayer information. The Direct Pay at IRS.gov was super-easy when I tried it. I also fill out SSA vouchers for clients to withhold taxes (max allowed at 22%). I suggest year-end RMD distributions with heavy withholding. My elderly clients are having difficulty remembering estimated payments. With interest rates for underpayment now higher (8% IRS 10% Virginia) estimated payments will be important this season.