You need to pay estimates if you won’t meet any of the exceptions to avoid an underpayment penalty. The best way to avoid being penalized is to pay 90% of the current year’s tax or 100% (110% if income over $150k) of your prior year’s taxes. Estimated taxes generally need to be made evenly over the year unless the income isn’t earned evenly over the year; in that case, you would complete and attach a Form 2210 to your personal tax return to annualize your income and show the IRS how much income you earned each quarter.