What will you owe for 2026?

From your latest pay stub's year-to-date column. Each paycheck left this year is added at the same size, so a bonus already paid isn't counted again and a raise already in is. Then Form 1040 in order: the $16,100 standard deduction ($32,200 married filing jointly), the brackets, $2,200 for each child under 17, self-employment tax and the business income deduction for a business, the 3.8% on investment income and the 0.9% Medicare surtax where they apply, and your state's own schedule.

The IRS adds a penalty when too little is paid during the year. Pay at least 90% of this year's tax, or 100% of last year's (110% if last year's income was over $150,000), through withholding and on-time estimated payments, and there is none, however the year turns out. Owing less than $1,000 at filing is never penalized.

Withholding counts as paid evenly through the year, whenever it actually comes out, so more withheld from the last few paychecks covers the earlier quarters too. A payment by January 15 covers only the last quarter. Line 4(c) of a new W-4 adds a fixed amount to each paycheck.

Capital gains count once you sell, so they are added in the app from a brokerage statement or by hand. Itemized deductions, education and energy credits, and income a stub doesn’t show (rentals, K-1s) are added there too, or read from last year’s return. State tax follows your state’s own deductions, exemptions and Social Security and pension rules, close but not a state return.

Not unless you make an account. The answers stay in your browser. With an account they become your tax profile, so the forecast opens on them and nothing is asked twice.