How this instrument works
A 401(k) projection is two calculations running side by side inside one formula. The balance already sitting in the account behaves like an ordinary lump sum: it compounds on its own, growing by the same (1+r)^n that any single deposit would follow. Every year's contribution is a separate, smaller deposit that only gets however many years remain until retirement to grow, so a dollar added in year one compounds far longer than a dollar added in year twenty-four — the annuity term in the formula sums up that whole staggered series at once rather than tracking each year individually.
The employer match here is defined as a flat percentage of Your annual contribution, $ — a matchRate of 50 means fifty cents added for every dollar contributed, with no salary-based ceiling built into the arithmetic. Real workplace plans almost always cap that formula, commonly phrased as '50% of the first 6% of pay,' so the field expects you to already know your own effective, capped rate rather than a headline number off a benefits page. Combined, contribution plus match becomes one annual deposit that compounds inside the same annuity term as the starting balance's own growth.
Three things sit outside this arithmetic on purpose. Contribution and return are both held constant for the entire span in Years until retirement, while real paychecks tend to grow and real markets never hold one steady rate. Employer match dollars are counted as fully yours the moment they're added, though many plans vest that money on a schedule and forfeit the unvested portion if you leave early. And the IRS caps how much can legally be deferred each year — this sheet performs the compounding regardless of what's typed into the contribution field, so it will not stop you from entering a figure above that legal ceiling.
- Enter what's already saved under Current balance, $ — the lump sum sitting in the account today.
- Set Your annual contribution, $ to the dollar amount you plan to add each year, not a percentage of pay.
- Enter Employer match (% of your contribution) as a plain percentage — 50 means fifty cents per dollar, already adjusted for any cap your plan applies.
- Set Expected annual return, % to the single fixed rate the whole projection compounds at.
- Enter Years until retirement, then read Projected balance for what the balance plus contributions plus match together reach.
Worked example — $20,000 plus a 50% match for 25 years
Take the default sheet: Current balance, $ at 20000, Your annual contribution, $ at 6000, Employer match (% of your contribution) at 50, Expected annual return, % at 7, and Years until retirement at 25. The match adds 6000 times 50 divided by 100, or $3,000 a year, so $9,000 of combined contribution and match lands in the account every single year on top of whatever the starting balance is doing on its own.
Split the formula in two and each half is checkable. The starting $20,000 compounds alone to $108,548.65 over 25 years at 7 percent — plain lump-sum growth, the same arithmetic a future-value sheet would return for that piece by itself. The $9,000 a year of contribution and match compounds through the annuity term to $569,241.34, since each year's deposit only earns however many years are left to run. Add the two pieces and Projected balance reads $677,789.99 — more than six times the lump sum alone, and most of the gap is money added along the way, not the balance the account opened with.
Questions
Does the employer match field include my plan's cap?
No — you have to supply it already capped. Employer match (% of your contribution) multiplies straight against whatever you type into Your annual contribution, $, with no salary-based ceiling built in. Real plans almost always cap the formula, commonly '50% of the first 6% of pay,' so work out your own effective, already-capped rate before entering it, or the projection overstates the free money on offer.
Does this check my contribution against the IRS limit?
No. The IRS caps elective deferrals at $24,500 for 2026 for savers under 50, plus an $8,000 catch-up for those 50 and older, adjusted most years. This sheet only performs the compounding arithmetic on whatever figure sits in Your annual contribution, $ — it will not flag or block an amount above that legal ceiling.
Is the employer match money mine right away?
Not necessarily. Many plans vest employer contributions on a schedule, and leaving before a set number of years can forfeit the unvested share entirely. Projected balance treats every dollar of match as fully yours from the day it's added — check your plan document for the real vesting schedule before treating that portion of the number as guaranteed.
How is this different from a plain compound-interest calculator?
A compound-interest sheet grows one deposit left untouched for the whole term. This one adds a second stream — contribution plus match, arriving fresh every year — that each compounds for only however many years remain, on top of the starting balance's own separate growth. That second stream is why a 401(k) balance often ends up mostly built from money added after day one, not the amount the account opened with.
Does the projection assume my contribution never changes?
Yes, for the entire span in Years until retirement. Real paychecks usually raise contribution amounts over a career, and real markets never hold one steady rate the way Expected annual return, % does here. Read Projected balance as what a level, unchanging scenario delivers, not a forecast of an actual, uneven working life.
Does this distinguish a traditional 401(k) from a Roth 401(k)?
No — the compounding arithmetic is identical either way. What differs is tax treatment: traditional contributions lower taxable income now and are taxed on withdrawal, while Roth contributions are taxed now and generally come out tax-free later. Projected balance shows pre-tax growth only; which account type keeps more of that final number after taxes is a separate question this sheet doesn't answer.
References
- IRS — Retirement topics: 401(k) and profit-sharing plan contribution limits
- Consumer Financial Protection Bureau — Planning for retirement
Read this first: This instrument shows arithmetic, not advice. Real offers add fees, taxes and terms that vary by lender and place — verify the figures against your actual paperwork before deciding anything.