401(k) Retirement Calculator

The 401(k) Calculator projects your plan balance year by year from your age now to your retirement age, applying your contribution percentage, your employer's match formula, annual salary increases, and your expected return — then totals your contributions, the employer's money, and investment earnings separately, and converts the result into a monthly retirement income. An inflation toggle restates everything in today's dollars.

How the Year-by-Year Model Works

For each year, the calculator takes your salary (grown by your annual raise), applies three steps, and rolls the balance forward:

$\text{Your Contribution} = \min(\text{Salary} \times \text{Contribution \%},\ \text{IRS Limit})$

$\text{Employer Match} = \text{Salary} \times \min(\text{Contribution \%},\ \text{Match Cap \%}) \times \text{Match \%}$

$\text{Interest} = \text{Starting Balance} \times \text{Return \%} \qquad \text{End Balance} = \text{Start} + \text{Interest} + \text{Contribution} + \text{Match}$

Two modeling choices to know: contributions and match are added at year-end, so interest for a year accrues on the starting balance only (a deliberately conservative convention); and the IRS elective-deferral limit is enforced — $23,500 under age 50,$31,000 at 50-plus in the stored settings, based on your current age. Monthly retirement income is the final balance divided by 240 — a 20-year drawdown.

Worked Example

Age 30 to 65, starting balance $10,000**, salary **$75,000 rising 2% a year, contributing 10%, employer matching 50% of the first 6%, return 7%:

• Year 1: contribution $7,500; match$75,000 × 6% × 50% = $2,250; interest$10,000 × 7% = $700; end balance **$20,450**.
• Year 2: salary $76,500; contribution$7,650; match $2,295; interest on$20,450 = $1,431.50; end balance **$31,826.50**.
• At 65: final balance $1,798,721**, composed of your **$374,959 of contributions, $112,488** of employer match, and **$1,301,275 of investment earnings.
• Monthly retirement income: $1,798,721 ÷ 240 = **$7,494.67**.

Read the composition: the market contributed more than you and your employer combined. And the match alone — money that exists only because you contributed at least 6% — is worth over $112,000 of contributions plus its own decades of compounding inside the earnings figure.

The Inflation Toggle

Run the same projection with inflation adjustment on (say 3%) and the final balance is divided by 1.03³⁵ — restating that $1.8M as roughly **$639,000 in today's purchasing power**, with contributions and match deflated the same way. Neither figure is "the real one" in isolation: nominal for comparing against future nominal goals, today's-dollars for judging the lifestyle it buys. Serious planning looks at both.

Limitations

The contribution limit is taken from your current age and held fixed — it does not step up when you turn 50 mid-projection or index for future IRS increases, and catch-up contributions beyond the stored limit are not modeled. Returns are constant; salary growth is a single smooth rate with no job changes or career breaks; fees inside plan funds are not deducted separately (fold them into a lower return assumption). Balances are pre-tax: traditional 401(k) withdrawals are taxed as income in retirement, which the projection does not net out. Roth 401(k) contributions are also not distinguished — the growth math is the same, the tax story is not.

Frequently Asked Questions

Am I contributing enough to get the full match?

Check the two percentages: you capture the full match only when your contribution percentage reaches the match cap (6% in the example). Contributing 4% against a 6% cap leaves a third of the match — in the example, $750 a year plus all its future compounding — unclaimed. It is the only guaranteed 50% (or 100%) return in the entire projection.

Why does year-1 interest look low?

Because of the year-end contribution convention: interest accrues on the starting balance for the full year, and the year's contributions begin earning from the next year. Real plans invest each paycheck, so actual earnings on contributions start sooner — treat the projection as slightly conservative rather than exact.

How is monthly retirement income calculated here?

As a straight 20-year amortization of the balance: final balance ÷ 240 months, with no further growth during drawdown and no tax. It is a scale indicator, not a withdrawal strategy — sustainable-withdrawal planning, Social Security timing, and required minimum distributions all refine it.