Methodology and accuracy
Every number on this site comes from a formula we will show you. Here they are, along with the IRS rules we follow and the limits of what a calculator can tell you.
- IRS-based rules
- Open formulas
- Client-side only
- Projected balance (at retirement)
- 1.846.072 US$
- Investment growth
- 1.366.123 US$
Why this site exists
What we are
401k Calculator is a set of free calculators for 401(k) retirement plans. There is no account system, no lead capture and no product we are paid to place at the top. The entire product is the arithmetic, done correctly, with the formula shown next to the result.
That matters more here than in most calculator categories, because 401k decisions are full of rules people get subtly wrong — the difference between the deferral limit and the total limit, when the 10% penalty applies, how the employer match cap works, and which age triggers required distributions. A calculator that shows its working lets you check the number rather than trust it.
We are not a bank, a broker, a plan administrator or a financial advisor, and we do not sell any product. Nothing on this site is financial, tax or investment advice.
The maths
Every formula we use
Future value with contributions
FV = B(1 + r)ⁿ + Σ Cₜ(1 + r)ⁿ⁻ᵗ
The main 401k calculator and the growth page: the starting balance and every future contribution compound at the expected return.
Employer match
Match = Salary × min(Your %, Cap %) × Rate
The match calculator: the employer pays a rate on your contributions up to a pay-percentage cap.
Early-withdrawal tax and penalty
Net = W − (W × 10%) − (W × Fed) − (W × State)
The withdrawal penalty calculator: ordinary income tax plus the 10% §72(t) additional tax before age 59½.
Roth vs traditional after-tax value
Roth = C·F vs Trad = C·F(1 − Tr) + (C·Tc)·F
The Roth vs traditional and Roth IRA vs 401k pages: comparing tax-free growth against a pre-tax deduction taxed later.
Required minimum distribution
RMD = Balance ÷ Life-expectancy factor
The RMD calculator: prior-year-end balance divided by the IRS Uniform Lifetime Table factor.
Retirement drawdown
Bₙ = Bₙ₋₁(1 + r/12) − Wₙ
The 'how long will it last' calculator: monthly returns less inflation-adjusted withdrawals until the balance runs out.
Conventions
The assumptions behind every calculation
Contribution limits use the IRS figures for the 2026 tax year: a $24,500 elective-deferral limit, an $8,000 age-50 catch-up (and $11,250 at ages 60–63), and a $72,000 combined §415(c) limit.
Investment returns are modelled as a steady average. Real markets are volatile, and the order of returns (sequence risk) affects outcomes, especially in retirement.
The employer match is modelled as a single tier — a rate up to one pay-percentage cap. Tiered and safe-harbor formulas are approximated by an effective rate.
Early-withdrawal figures assume pre-tax (traditional) dollars and no §72(t) exception, using the marginal tax rate you enter without re-banding.
Projected balances are shown before tax, in nominal dollars. Inflation reduces real purchasing power, and traditional balances are taxed on withdrawal.
RMDs use the Uniform Lifetime Table on the prior-year-end balance; a different table applies if your sole beneficiary is a spouse more than 10 years younger.
Worked through
The core calculation, step by step
FV = B(1 + r)ⁿ + Σ Cₜ(1 + r)ⁿ⁻ᵗ
The future-value formula that sits underneath every projection on the site.
- FV
- Future value — your balance at retirement
- B
- Your 401k balance today
- r
- Expected average annual return
- n
- Years until retirement
- Cₜ
- Employee + employer money added each year
Step by step
- 1
Grow the current balance at the expected return for all the years remaining.
- 2
Each year, add your contribution (salary × your percentage) plus the employer match.
- 3
Cap your contribution at the age-adjusted IRS deferral limit.
- 4
Compound each year's contribution for the years left until retirement.
- 5
Add it all together for the projected balance.
- 6
Subtract total contributions to isolate investment growth.
Limits
What this calculator cannot tell you
It cannot tell you your actual investment return. Returns depend on your fund choices and the market, and every projection here depends on the average you assume being roughly right over the long run.
It cannot tell you your exact tax. Brackets are progressive and change over time, a large withdrawal can push you into a higher band, and state rules vary. The calculators use the flat marginal rate you enter.
It cannot tell you your plan's exact rules. Match formulas, vesting schedules, loan provisions and hardship rules are set by your employer's plan document, which takes precedence over any figure here.
For those questions, speak to a qualified financial or tax professional and confirm all details with your plan administrator before acting.
Formulas and content last reviewed . IRS limits change each year — confirm current figures at IRS.gov and with your plan administrator.
Security & privacy
Your numbers never leave your browser
IRS-accurate formulas
Uses the current IRS contribution limits, penalty rules and RMD tables — updated for 2026.
100% free, no login
No signup, no email wall, no paywall. Every calculator is fully usable on first visit.
Your data never leaves your browser
Every calculation runs client-side in JavaScript. Nothing is sent to a server or stored.
Served over HTTPS with no mixed content. Read our privacy policy or see the formulas and methodology behind every figure.
Keep exploring
Explore the rest of the site
- 401k CalculatorThe main retirement projection — salary, contribution, match, and your balance at retirement.
- 401k Growth CalculatorProject what your 401k will be worth at retirement — including your contributions, the employer match, and decades of compound growth.
- 401k Match CalculatorSee exactly how much free money your employer adds to your 401k — and the contribution rate you need to capture every dollar of the match.
- Roth vs Traditional 401k CalculatorCompare the after-tax retirement value of Roth and traditional 401k contributions side by side — and see which one leaves you with more.
- Guides (15)Long-form explanations of how 401(k)s work, compared against the alternatives.
- 401k glossaryEvery term defined, with the rule or formula attached wherever one applies.
- FAQ hubDirect answers to the questions people actually ask about 401(k)s.
- Full sitemapEvery page on the site in one index, plus the XML sitemap.
Check the numbers yourself
Every formula above is live in a calculator on this site. Enter your own figures and compare the result against your plan statement.