401(k) Calculator

The 401(k) is a tax-advantaged employer-sponsored retirement savings plan available to employees of private-sector companies in the United States. Named after the section of the Internal Revenue Code that established it, the 401(k) allows workers to contribute a portion of their pre-tax salary to a personal retirement account, where the funds can be invested in mutual funds, index funds, and other assets. Because contributions reduce taxable income in the year they are made—and because investment earnings compound without being taxed until withdrawal—the 401(k) is one of the most powerful wealth-building tools available to American workers.

How This Calculator Works

This calculator projects your 401(k) balance at your target retirement age by simulating annual growth. Each year, your existing balance compounds at the expected annual return rate. Employee contributions (based on your salary and contribution rate) and employer match contributions are added mid-year, also compounding at half the annual rate to approximate continuous contributions throughout the year.

The employer match is calculated by taking the lower of your contribution rate and the employer match limit, then multiplying by the employer match rate. For example, if you contribute 8% of salary, the employer matches 50% of contributions up to 6% of salary, your effective employer contribution is 3% of salary (6% × 50%).

Once your projected balance is calculated, the 4% rule estimates the sustainable annual withdrawal by multiplying your balance by 4%. Dividing by 12 gives the estimated monthly retirement income. This widely referenced guideline—developed from historical portfolio research—suggests that a retiree following this withdrawal rate has a high probability of not outliving their savings over a 30-year retirement.

Employee Contributions and IRS Limits

In 2025, the IRS sets the annual employee contribution limit for 401(k) plans at $23,500. Employees aged 50 and older may make additional catch-up contributions, bringing their total to $31,000. These limits apply to elective deferrals (pre-tax and Roth 401(k) contributions combined) and are adjusted periodically for inflation.

Your contribution rate is expressed as a percentage of your gross salary. A common target is to contribute at least enough to capture the full employer match—commonly called 'leaving money on the table' when the match is not fully utilized. Beyond the match, many financial planning guidelines suggest targeting a total savings rate of 15% of gross income (including employer contributions) for retirement.

The Power of Employer Matching

Employer matching is a direct supplement to your retirement savings provided by your employer, and it represents an immediate, guaranteed return on your contribution. A common matching formula is 50 cents on the dollar up to 6% of salary, meaning an employee who contributes 6% of salary receives an additional 3% from their employer—effectively a 50% instant return on that portion of savings.

Employer match terms vary widely. Some employers match dollar-for-dollar up to 3–4% of salary. Others have more complex tiered structures. Match contributions may be subject to a vesting schedule, meaning employees must remain with the employer for a certain number of years before the match is fully owned. Understanding your employer's match formula and vesting schedule is essential to optimizing the value of your 401(k).

This calculator allows you to specify both the match rate (how many cents per dollar the employer contributes) and the match limit (the maximum percentage of salary eligible for matching). By modeling the full employer contribution, the projection shows the substantial difference that employer matching makes over a multi-decade savings horizon.

Compound Growth Over Time

Compound interest—earning returns not only on your principal but also on previously accumulated earnings—is the central force that transforms modest regular contributions into a substantial retirement nest egg. The longer the compounding period, the more powerful the effect. A worker who begins contributing to a 401(k) at age 25 and retires at 65 has 40 years of compounding, while one who starts at 35 has only 25 years.

As a rough illustration, consider two workers both earning $75,000 who contribute 6% of salary with a 3% employer match and expect a 7% annual return. Worker A starts at age 25 with a $10,000 existing balance; Worker B starts at 35 with the same balance. At retirement age 65, Worker A may accumulate roughly twice what Worker B accumulates—despite contributing for only ten additional years. This gap illustrates the mathematical dominance of time in compound growth.

Choosing an Expected Return Rate

The annual return rate is the single most sensitive assumption in any long-term projection. Over rolling 30-year periods, diversified equity portfolios have historically delivered average annual returns of roughly 7–10% before inflation. However, past performance does not guarantee future results, and actual returns in any given period depend on market conditions, portfolio allocation, fees, and other factors.

For conservative long-term projections, many financial planners recommend using a nominal return of 5–7% to build in a margin of safety. Investors with portfolios weighted toward bonds or stable assets should use lower rates. The calculator allows you to test multiple scenarios by changing the return rate to see how sensitive your projected balance is to this assumption.

The 4% Withdrawal Rule

The 4% rule originated from research published in the 1990s by financial planner William Bengen, who studied historical stock and bond return data to determine sustainable withdrawal rates for 30-year retirements. His analysis found that a portfolio of 50–75% equities could sustain annual withdrawals of 4% of the initial balance (adjusted annually for inflation) across all historical 30-year periods without being depleted.

This calculator applies the 4% rule by multiplying the projected retirement balance by 4% to estimate annual income, then dividing by 12 for a monthly figure. The result provides a reference point for how much income your savings may support. Actual sustainable withdrawal rates depend on retirement duration, investment allocation, tax situation, and other income sources such as Social Security. For personalized retirement income planning, consulting a qualified financial adviser is recommended.

Traditional 401(k) vs. Roth 401(k)

Many employers now offer both traditional and Roth 401(k) options. Traditional 401(k) contributions are made with pre-tax dollars, reducing your taxable income today, but withdrawals in retirement are taxed as ordinary income. Roth 401(k) contributions are made with after-tax dollars, so withdrawals in retirement—including all investment gains—are generally tax-free.

The choice between traditional and Roth depends largely on whether you expect to be in a higher tax bracket during your working years or in retirement. If you expect your tax rate to be lower in retirement, the traditional 401(k) generally provides a greater tax benefit. If you expect your tax rate to be higher in retirement, the Roth option may be more advantageous. This calculator does not model the tax treatment of contributions or withdrawals, as that depends on individual tax circumstances.

Factors This Calculator Does Not Cover

This calculator projects nominal (pre-inflation) balances. In real purchasing power, a dollar today will be worth less in 30 years due to inflation. To approximate inflation-adjusted results, subtract the expected average inflation rate from your return rate before entering it. For instance, entering 4% instead of 7% with 3% expected inflation gives a rough estimate of your balance in today's purchasing power.

The calculator also does not model Social Security benefits, required minimum distributions (RMDs) that begin at age 73 under current law, account fees, salary growth over time, or changes in contribution rates. All of these factors can significantly affect real-world retirement outcomes. This tool is intended for educational estimation purposes. For a comprehensive retirement plan tailored to your circumstances, consulting a qualified financial adviser is advisable.