THE NUMORIX GUIDE
How to use the 401(k) calculator
Last reviewed September 14, 2026
What this calculator does
The projection runs one year at a time.
Formula and method
The projection runs one year at a time. Employee contribution is the lesser of salary times the contribution percentage and the engine's 2025 deferral limit plus age-based catch-up amount. Employer match is the lesser of employee contribution times match percentage and salary times the match limit. The balance then grows by annualReturn. The early-withdrawal tab subtracts the entered federal, state, and local rates and applies a simplified 10% penalty test.
Variables and inputs
Projection inputs are current age, salary, current balance, employee contribution percent, employer match percent and limit, retirement age, life expectancy, salary increase, annual return, and inflation. Early withdrawal inputs are withdrawal amount, three tax rates, employment status, age-55 status, disability status, and other exemptions.
Worked example
At age 30 with $75,000 salary, $25,000 balance, 10% contribution, a 50% match capped at 6% of salary, and 7% return, employee contribution is 75,000 x 0.10 = $7,500. Match is min(7,500 x 0.50, 75,000 x 0.06) = $3,750, so year-one balance is (25,000 + 7,500 + 3,750) x 1.07 = $38,762.50.
How to interpret the result
The projection separates employee contributions, employer match, and modeled investment growth. The early-withdrawal result is the cash remaining after the rates and any modeled penalty, not the amount that an actual plan administrator or tax return must use.
Common mistakes to avoid
Check whether a match percentage means a match rate or a percentage of salary. Do not assume the match is unlimited. For a withdrawal, distinguish income-tax withholding from the separate additional-tax rules that may apply to an early distribution.
Assumptions and limitations
The projection hardcodes a 2025 deferral limit and simplified catch-up amounts, uses annual contributions, and does not model vesting, plan-specific match formulas, fees, salary caps, required distributions, Roth taxation, or market volatility. The penalty tab is an educational approximation and should not determine whether a distribution is permitted.