If additional tax withholding is needed to avoid needing to annualize income to avoid an underpayment penalty, you can increase tax withholding from sources of income that you will receive between now and the end of the year. Unlike estimated tax payments which are credited when paid, tax withholding is treated by default as received evenly throughout the year. This means that increased tax withholding later in the year can make up for what would be considered underpayment earlier in the year absent annualization of income. You can even potentially manufacture tax withholding by doing an indirect rollover of a qualified retirement account.
