What your 401(k) will actually be worth at retirement
The 401(k) number most people carry in their head — "my match is 5%, I'll be fine" — is off by hundreds of thousands of dollars in either direction. The actual balance depends on four numbers: starting balance, total contribution rate (yours plus match), years, and real return. Change any one by a percentage point and the final balance moves by six figures over a career.
This tool compounds the starting balance forward and adds the annual contribution (your % + the employer's %) as a growing stream. The "Balance at retirement" output is pre-tax. Multiply by roughly 0.75–0.80 to get a spendable number — most 401(k) dollars come out as ordinary income when you retire and pay federal plus state tax. Your effective retirement rate is usually lower than your working rate; see the Retirement Tax Planning Calculator for the full picture.
Worked example: $90k salary, 10% + 5% match, 25 years
Salary $90,000, your 10% = $9,000, employer's 5% match = $4,500, combined $13,500 a year. Starting balance $85,000. Compound 25 years at 7%: the $85,000 grows to $461,000, and the $13,500-a-year stream compounds to $854,000. Total: $1,315,000 pre-tax. The employer match alone — $4,500 a year — adds $285,000 to that figure. Never, ever leave the full match on the table.
Now vary the numbers: bump your 10% to 15% and the balance jumps to $1,635,000. Drop the return to 5% and it falls to $1,005,000. The two big levers are again savings rate and time. Use the Employer Match Calculator to size the match you may still be leaving behind.
The three things your 401(k) plan menu hides
One: fund expenses. A low-cost index fund is 0.03–0.08%. A "target-date" fund at a legacy plan might be 0.60% or more. On $500,000 over 25 years, that is about $75,000 of fees you would rather not pay. Check your Summary Plan Description. Two: the vesting schedule. Some employers vest match over 3–6 years. If you plan to leave in 2 years, budget on your vested balance, not the paper balance. Three: the "true-up" rule. If you front-load contributions to hit the IRS limit early, some plans stop matching once you stop contributing. Check whether your plan has a year-end true-up; if not, spread contributions across every paycheck.
Mega-backdoor Roth: the advanced move most miss
If your plan allows after-tax (non-Roth) contributions plus in-service conversions, you can stuff an extra $30,000+ per year into Roth space — far more than the $23,000 base limit. That "mega-backdoor Roth" is the single biggest tax-advantaged move for high earners. Call HR or read the SPD: look for "after-tax contributions allowed" and "in-service distributions allowed." If both are yes, route those contributions and convert immediately. Pair with the IRA Rollover & Roth Conversion Calculator to model the long-term benefit.
When to leave dollars in the 401(k) after you retire
Most people instinctively roll the 401(k) to an IRA the day they retire. Sometimes that is wrong. Reasons to leave it: stable-value funds (hard to replicate in an IRA), lower cost institutional share classes, age-55 rule (penalty-free withdrawals if you separated at 55+ and keep it in the 401(k)), and stronger creditor protection under ERISA. Reasons to roll: bigger fund menu, Roth conversions easier, consolidation of accounts. Run the math on both before deciding. The IRA Rollover Calculator handles the conversion side; the Required Minimum Distribution Calculator handles the post-73 side.
Common mistakes this tool helps you avoid
Three mistakes wreck most 401(k) plans. One: planning on 10% returns. The S&P 500 averaged ~10% nominal since 1928, but inflation and 0.5% fund fees bring that to roughly 5.5–6% real. Run the 10% number and you will be underfunded by 20–30% in any realistic outcome. Two: ignoring taxes on the way out. A $1,000,000 pre-tax 401(k) is $750,000–$800,000 spendable for most households once federal and state tax come out. Three: treating Social Security as fixed. Claiming at 62 pays 70% of your primary insurance amount; waiting to 70 pays 124%. On a $2,400 PIA that is $1,680 vs $2,976 a month — a $15,552-per-year, lifelong spread.
When to hire a professional
Use this calculator to get a directional answer in five minutes. Hire a fee-only fiduciary CFP (search NAPFA, XY Planning Network, or Garrett) when the 401(k) decision involves any of these: portfolio over $750,000, a defined-benefit pension with a lump-sum option, rental property, concentrated stock (ISOs, RSUs, founder shares), a blended family, special-needs planning, or a move across a state line. A $3,000 one-time plan typically recovers its cost many times over in avoided tax and claim-timing mistakes.
For a simpler situation — single account, single state, standard Social Security — this tool plus an annual self-review is fine. Re-run every October so you still have time to act on the year.
Disclaimer
This is not financial, tax, investment, or legal advice. Calculations are educational and rely on the inputs you provide. Tax brackets, contribution limits, Social Security PIA bend points, RMD factors, and Medicare IRMAA thresholds change — verify against the official IRS, SSA, and CMS tables before acting on any number. Past investment returns do not predict future results. For a legally binding plan, engage a licensed fiduciary, CPA, or estate attorney.
About this calculator
This tool runs entirely in your browser — nothing you type is logged, stored, or sent to a server. Use Export PDF to save a clean copy of your inputs and results for a spouse, advisor, or your own records. Missing a 401(k) scenario you need? Email us at hello@retirementhub.dev and we will add it.