What this calculator is doing
A federal refund is not a bonus from the Treasury. It is the difference between what you already paid (withholding plus estimated payments) and the tax that remains after credits. If you paid more than that net tax, the difference comes back as a refund. If you paid less, the difference is a balance due with the return you file in 2027.
The tool starts with the income you enter, subtracts above-the-line adjustments, then subtracts the larger of the 2026 standard deduction (plus any extra amount for age 65 or blindness) or the itemized total you typed, plus any other below-the-line amount such as a Schedule 1-A figure you already computed on NewDeduct. It taxes ordinary taxable income with the 2026 rate tables in Revenue Procedure 2025-32 and applies the 0%, 15% and 20% rates to long-term capital gains and qualified dividends using the stacking method on the same document. It then applies the Child Tax Credit, the credit for other dependents and the Earned Income Credit, using the 2026 dollar amounts from that revenue procedure.
Worked example
A single filer under 65 with $60,000 of wages, no children and the standard deduction of $16,100 has $43,900 of taxable income. The 2026 single table taxes the first $12,400 at 10% ($1,240) and the next $31,500 at 12% ($3,780), for $5,020 of income tax. If box 2 withholding is $5,500, the sketch shows a $480 refund. Change withholding to $4,000 and the same tax becomes a $1,020 balance due. The numbers update as you type, so you can see how an extra qualifying child or a larger 401(k) adjustment would move the result.
What you should still check by hand
Eligibility for the Child Tax Credit and EITC depends on residency, Social Security numbers, relationship and support tests that a browser form cannot verify. Married people filing separately are generally ineligible for the EITC; the tool returns zero for that status and does not model the narrow separated-spouse exception. The additional Child Tax Credit uses the 15%-of-earned-income formula and the $1,700 per-child cap; it does not run the alternative formula on Schedule 8812 for some families with three or more children. If you have self-employment income, add the self-employment tax you expect to “other taxes” and the deductible half to adjustments, or the refund will be too high.
For official filing, start with IRS Free File if you qualify, or software that supports every form you need. To change 2026 withholding before year-end, use the IRS Tax Withholding Estimator and a new Form W-4.