401k Calculator

What is a 401k and how does it work?

A 401(k) is one of the most powerful retirement savings tools available to American workers. Named after the section of the Internal Revenue Code that governs it, the 401(k) plan allows employees to direct a portion of their pre-tax earnings into a dedicated retirement account. This pre-tax treatment reduces your taxable income today, while the invested funds grow tax-deferred until you withdraw them in retirement.

Most 401(k) plans offer a selection of mutual funds, index funds, and other investment vehicles. You choose how to allocate your contributions among these options based on your risk tolerance and time horizon. The longer your money remains invested, the more it benefits from the compounding of investment returns — a process often described as earning returns on your returns.

When you retire and begin making withdrawals, the money is taxed as ordinary income. If you expect to be in a lower tax bracket in retirement than you are today, the traditional 401(k) tax deferral strategy works very much in your favor. This makes the 401(k) especially valuable for mid-to-high earners who want to reduce their current tax burden while building long-term wealth.

How employer matching accelerates your savings

Employer matching is arguably the most valuable benefit of participating in a 401(k). When your employer matches your contributions, they are essentially giving you a guaranteed 50% or 100% return on that portion of your savings before a single investment gain is made. Not taking full advantage of employer matching is one of the most costly financial mistakes a worker can make.

A typical matching formula is a 50–100% match on contributions up to a certain percentage of your salary — for example, "100% match on the first 4% of salary." If your salary is $80,000 and you contribute 4% ($3,200), your employer adds another $3,200, giving you $6,400 contributed in that year alone before any investment growth is calculated.

It is worth noting that many employer matching contributions are subject to a vesting schedule, meaning you must work at the company for a certain number of years before you fully own the matched funds. Vesting schedules vary — some are immediate, others are graded over three to six years. Always review your plan's vesting terms before making career decisions that could forfeit unvested employer contributions.

2025 contribution limits and catch-up contributions

The IRS sets annual limits on how much you can contribute to your 401(k). For 2025, the employee elective deferral limit is $23,500. The combined limit across employee and employer contributions is $70,000. Workers aged 50 or older can contribute an additional $7,500 as a catch-up contribution, raising their personal limit to $31,000.

These limits apply per person across all 401(k) plans — if you have accounts from multiple employers in the same year, your total employee contributions cannot exceed the annual limit. The IRS typically adjusts these limits each year to account for inflation. Checking the IRS website at the start of each year ensures you are aware of the latest figures when planning your contribution rate.

If your budget does not allow you to max out your 401(k) immediately, a practical strategy is to increase your contribution percentage by 1% each year, particularly after receiving a raise. Many plans offer an auto-escalation feature that does this automatically, making it a painless way to build toward the maximum limit over time.

What return rate should I use for my 401k projection?

The annual return rate you use in your 401(k) projection has a significant impact on the final projected balance. Historically, a broadly diversified portfolio of U.S. equities has returned approximately 7–10% annually on a nominal basis. After adjusting for inflation, the real return has historically been closer to 5–7%.

Financial planners often suggest using a conservative estimate of 6–7% for long-term retirement projections to avoid overestimating your final balance. Your actual return will depend on your chosen investment allocation — a portfolio heavy in equities will typically have higher expected returns but also greater short-term volatility compared to a more conservative bond-heavy allocation. As you approach retirement, many advisors recommend gradually shifting toward a more conservative allocation to protect the gains you have accumulated.

Traditional vs Roth 401k: which is right for you?

Many employers now offer both traditional and Roth 401(k) options within the same plan. The fundamental difference comes down to when you pay taxes. With a traditional 401(k), contributions are made pre-tax, reducing your taxable income in the year you contribute. You then pay income tax on withdrawals in retirement. With a Roth 401(k), contributions are made with after-tax dollars, but qualified withdrawals — including all the accumulated growth — are completely tax-free in retirement.

If you are early in your career and expect your income and tax rate to rise significantly over time, a Roth 401(k) can be an excellent choice, as you lock in tax payments at today's potentially lower rate. If you are in a high income bracket today and expect a lower income in retirement, a traditional 401(k) gives you a valuable tax break now. Many people choose to split their contributions between both types for tax diversification — essentially hedging against future changes in tax law or personal income.

Unlike Roth IRAs, Roth 401(k) accounts were historically subject to Required Minimum Distributions (RMDs), but the SECURE 2.0 Act eliminated RMDs for Roth 401(k) plans starting in 2024, making them even more attractive for those who want to let their savings continue growing tax-free throughout retirement.

The power of starting early: compound growth in a 401k

One of the most compelling arguments for starting your 401(k) contributions as early as possible is the power of compounding. When your investment returns are reinvested, they generate their own returns in subsequent years, creating a snowball effect that accelerates dramatically over time.

Consider two workers: one starts contributing $6,000 per year at age 25, and another starts at age 35. Assuming a 7% annual return, the worker who started at 25 would accumulate roughly $1.37 million by age 65, while the worker who started at 35 would accumulate approximately $680,000. Despite contributing for 10 extra years and putting in an additional $60,000 out of pocket, the early starter ends up with more than double the retirement balance — all because of compound growth over those extra 10 years.

This is why financial advisors consistently emphasize starting contributions as early as possible, even if the initial amounts are small. The time value of money makes early contributions disproportionately more valuable than later ones. A $1,000 contribution at age 25 is worth far more in retirement than a $1,000 contribution at age 45.

How to maximize your 401k

Getting the most out of your 401(k) involves more than just contributing regularly. Always contribute at least enough to receive your full employer match — this is a guaranteed return on investment that no other savings vehicle can match. Second, increase your contribution rate each time you receive a raise, so your lifestyle does not absorb the entire increase. Third, review your investment allocation at least annually to ensure it reflects your current risk tolerance and time horizon.

Most plans offer target-date funds that automatically adjust your allocation as you age, which can be a convenient set-and-forget option for those who do not want to actively manage their investments. If you are over 50, take advantage of the catch-up contribution provision to accelerate your savings in the critical decade before retirement. Finally, resist the temptation to take early withdrawals or loans from your 401(k), as both carry significant financial penalties and permanently reduce the compounding runway available to your savings.

Early withdrawal rules and penalties

Taking money out of your 401(k) before age 59½ typically triggers a 10% early withdrawal penalty on top of ordinary income taxes on the withdrawn amount. For someone in the 22% federal tax bracket, that adds up to a 32% effective tax hit — meaning a $10,000 withdrawal nets only around $6,800 after taxes and penalties. This makes early withdrawal one of the most expensive ways to access cash and should be avoided whenever possible.

There are limited exceptions to the early withdrawal penalty, including total and permanent disability, certain unreimbursed medical expenses, qualified domestic relations orders in a divorce, and separation from service at age 55 or older. Some plans also permit hardship withdrawals for specific financial emergencies, though these are still taxed as ordinary income. If you need to access funds before retirement, a 401(k) loan may be preferable to an outright withdrawal — you repay yourself with interest — though it still carries risks if you leave your employer, as the outstanding balance may become immediately taxable.