If you owe more than $1000 next tax time, you can be assessed a penalty for not having enough tax withheld during the year, even if you pay in full when you file. To avoid this problem, you can adjust your withholding, or make estimated payments. If you make estimated payments online at www.irs.gov/payments, you don't need the vouchers, because your online payment is recorded under your SSN. You only need the vouchers if mailing a paper check. The amount of the vouchers may not be correct for your situation, as they are only based on your 2020 information. Depending on your income and withholding for 2021, you might owe more or less than estimated on the vouchers.
