Can I use extra paycheck withholding instead of paying quarterly estimates?

Yes, and it's often the cleanest fix if you or a spouse has a W-2 job. Withholding is treated by the IRS as paid evenly throughout the year no matter when it's actually taken, so a big withholding bump late in the year can retroactively cure an underpayment that quarterly estimates cannot. If you have significant side income, capital gains, or RMDs, you can increase withholding on a W-2 paycheck (or ask for extra tax to be withheld from an IRA distribution or a year-end bonus) rather than juggling four estimated payments. Adjust it using a fresh Form W-4 with an extra dollar amount on the appropriate line. This trick is especially useful in December when you realize you're short. Review the IRS Tax Withholding Estimator on irs.gov to size it correctly.