To avoid underpayment penalty you need to pay thru the year via withholding or timely (usually quarterly) estimated tax (ES) payments, the smaller of - 100% of prior year tax (110% if prior year AGI was > 150k or 75k if filing MFS), or 90% of current year tax
Turbotax by default will generate vouchers based on the prior year tax method and assuming 2026 withholding is the same as 2025. If you expect a drop in income for 2026 then this is likely an overestimate as you would want to pay 90% of current year tax. These vouchers are not part of your filing and are not mandatory to pay you can ignore them or recalculate them (in any case try to pay ES electronically at irs.gov or your state tax website rather than mailing checks and vouchers).
Under Other Tax Situations / Form W4 and Estimated Taxes you can provide estimates for 2026. With a caveat there have been some complaints in this forum that it's not taking into account withholding estimate for 2026 - I don't use it so not entirely sure the issue, but just be careful to check the calculations. Or any tax calculator will do (see below), you just need to have a process to estimate your 2026 taxes then take 90% of that, subtract withholding and divide by 4. If in doubt err on overpaying earlier quarters and you can always reduce payments later in the year as you refine your estimate, any overpayments from earlier quarters will carry forward to later quarters, but you can't make up for an underpayment in earlier quarters (just resolve it as soon as you can to stop the penalty accruing). Any increase in withholding even later in the year is always considered "timely" and evenly applied to the entire year by the IRS, and will reduce your total ES due.
try this calculator
https://www.dinkytown.net/java/1040-tax-calculator.html
See also IRS instructions for Form 2210 and 1040-ES.
