401(k) Tax Savings Calculator

401(k) Tax Savings Calculator takes the most important numbers in a 401(k) tax savings decision and surfaces the answer in seconds. Tax is an optimization problem — small changes in deductions, timing, or filing status can swing the outcome by thousands of dollars. The calculator makes the math explicit so you can plan, not guess.

Enter your numbers. The results update live. Try a few scenarios — conservative, expected, and optimistic — to see how sensitive the answer is to each input. Export the PDF and hand it to your CPA as a starting point.

• Use your latest pay stub or 1099 for the most accurate numbers.
• Re-run this before year-end so you can act on what you find (bump up 401(k), harvest losses, bunch charitable gifts).
• Double-check with a CPA before filing or making major decisions.

Confusing your marginal bracket with your effective rate is the most common 401(k) tax savings mistake. Your marginal rate is what you pay on the next dollar you earn. Your effective rate is what you paid on the whole pile. They are usually 5–10 percentage points apart. Decisions about deductions and Roth conversions depend on the marginal rate; decisions about cash flow and overall liability depend on the effective rate. Know which is which.

Federal tax depends on filing status, taxable income (gross minus above-the-line adjustments and deductions), credits you qualify for, and special items like capital gains, QBI, AMT, and NIIT. State tax layers on top and varies wildly — Florida and Texas have zero state income tax; California and New York can add 10%+.

This calculator uses 2025 brackets and commonly accepted assumptions. It is not a substitute for filing software or a professional.

This is not tax or financial advice. The calculator is for educational purposes. Tax law is complex, changes frequently, and depends on facts specific to you (state of residence, filing status, dependents, prior-year carryovers). Consult a licensed CPA or tax attorney before filing or making decisions based on these numbers.

This tool runs entirely in your browser. Nothing you type is sent to a server or stored anywhere. Use it as many times as you like for as many scenarios as you like. If there's a 401(k) tax savings calculator you wish existed, email us via the contact page.