401(k) Calculator

Worked example

Example: with about $25,000 saved today, roughly $500/month employee contributions, a 50% employer match, near 7% average annual return, and a 20-year horizon, many plans project a balance in the low-to-mid hundreds of thousands of dollars—your plan rules and market returns will differ.

How it works

Projects a 401(k) balance with monthly compounding. Employee contributions are added each month; employer match is calculated as a percentage of the employee contribution and added monthly. Starting balance grows with the same monthly return. IRS annual limits, vesting schedules, catch-up contributions, plan fees, and tax treatment are not modeled.

Limitations

Employer match rules, IRS limits, and catch-up contributions are simplified. Consult your plan documents for exact eligibility.

Privacy and file handling

Your data stays on your device and is not uploaded.

Accuracy & methodology

This section documents how the calculator works, what it leaves out, and when results were last reviewed. Figures are educational estimates—not professional advice—and are not labeled "current" unless tied to automatically updated reference data.

Formula source or methodology

Monthly compounding at annual return ÷ 12. Starting balance grows each month. Employee contribution is deposited monthly; employer match = employee contribution × match%. Total monthly deposit uses the future value of an ordinary annuity (payments at end of month) plus FV of starting balance.

Jurisdiction

United States (educational projection only)

Unit system

US dollars; monthly contribution and balance fields

Rounding method

Currency amounts round to two decimal places (half up via Math.round × 100 / 100).

Assumptions

• US 401(k) planning context; user-entered return rate is constant for the full horizon
• Employer match is a flat percentage of the employee contribution every month
• Same monthly return applies to existing balance and new deposits
• Contributions continue uninterrupted for the entire period

Known omissions

• Not tax, legal, investment, or lending advice. Confirm material decisions with qualified professionals.
• 2026 IRS contribution limits ($23,500 elective deferral; $7,500 catch-up age 50+; $70,000 combined annual additions under §415(c)) — limits are not enforced in the model
• Employer match annual caps, true-up provisions, and vesting schedules
• Plan administrative fees and fund expense ratios
• Inflation adjustment of future dollars (nominal dollars only unless stated)
• Income tax on withdrawals (pre-tax vs Roth treatment)
• Required minimum distributions (RMDs) and early withdrawal penalties
• Beginning- vs end-of-pay-period contribution timing beyond end-of-month annuity model
• Automatic enrollment escalation or bonus/true-up deposits

Test cases (automated)

• Valid inputs ($25k balance, $500/mo employee, 50% match, 7% return, 20 years) produce a positive projected balance
• Negative balance, negative contribution, or invalid match % are rejected

Version & last verified

Logic version 1.0. Content and formulas last verified 2026-07-24.

Important notice

Results are estimates for educational purposes and are not financial advice. Contribution limits, vesting, taxes, and fees are simplified or omitted. Consult a qualified financial professional for personal guidance.