With TurboTax Online, you can preview your return before you file to see how your taxes were calculated. See here for details.
Taxes are often calculated using a different method than the tax tables. For example, if you have capital gains, the tax on those is calculated at the capital gain rate for your income level. If you are self-employed, you may have self-employment taxes in addition to income taxes.
As stated in this TurboTax help article:
Instead of a refund meter at the top of your screen, you’ll see your refund or taxes due in the Federal Review section of TurboTax Online. For accuracy and simplicity, we show these totals after you enter your income, deductions, and credits instead of a running refund tracker at each step of the filing process.
This change was made for the tax year 2024 products.