Looking forward. In early January 2025 I sold stock having a significant capital gain. How do I handle fit withholding?

[MaryK4]

You can go to the Estimated Taxes section in TurboTax and enter the information to get an estimate of what you should be paying in estimated taxes.  You can also choose to increase withholding from your pay if you have a job and want to pay through the year.   See Tax Withholding Estimator and provide your employer with an updated W4.  Estimated taxes can be difficult since they are dependent on your other income, so it is a good idea to check it again throughout the year if you have any changes that were not unexpected.