Do you really mean that you want to calculate your tax for 2026, or do you mean that you want to calculate your tax for the 2025 tax return that you will file in 2026?
Either way, realistically you can't do it right now. The tax and spending bill currently being considered in Congress is likely to make significant changes in the income tax laws for 2025 and later. Without knowing what the final bill will contain, any calculation that you do now would be just a guess.
Why do you want to calculate your 2026 (or 2025) tax now?