IRS requires you to estimate your Required Annual Payment for the year and pay as you go.
Assuning you have no W-2 withholding nor other withholding,
you can base your estimate on prior year's tax , or 90% of this year's tax, whichever is smaller.
each quarter your withholding and estimated tax paid must be at least 25% of the estimate, even if your income is uneven, [Otherwise, you will be penalized.] this is the simplified method, default.
if your estimate is based on this year's tax and turns out to be wrong you may be penalized.
you can compensate by overestimating.
if your estimate is based on prior year's tax, you know that when you file by April 15, which is also the first estimated tax payment due date. How convenient.
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@lmb4gr
See IRS make a payment page to pay Estimate Tax Payment No.1.
Your estimate may be different from the TurboTax estimate.
