The IRS levies underpayment penalties if you don't withhold or pay enough tax on income received during each quarter. Even if you paid your tax bill in full by the April deadline or are getting a refund, you may still get an underpayment penalty.
To annualize your income, search for annualizing your tax (use this exact phrase) to be taken to the underpayment penalty section in TurboTax.
See the example in this FAQ. @GregorL
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