About the 401(k) Calculator
A 401(k) is a compound growth problem wrapped around one feature that is not a growth problem at all: the employer match.
A 50% match is an immediate 50% return. A dollar-for-dollar match is 100%. Both are credited the moment you contribute, guaranteed, with no market risk and no waiting. Nothing else available to an ordinary saver is remotely comparable.
So the most consequential number this calculator produces is not the projected balance. It is how much match is being left behind by someone contributing below the threshold — and how much that costs over a career.
How to Use the 401(k) Calculator
This 401k calculator needs five things about your plan, and the two that describe the match do most of the work.
Enter your salary and what you contribute as a percentage.
Then the match, which has two parts and both matter:
Employer matches — the rate. 50% means fifty cents per dollar you put in; 100% is dollar for dollar.
Match applies up to — the salary percentage the match stops at. "50% up to 6%" means the employer pays half of what you contribute, but only on the first 6% of your salary.
The annual contribution limit caps your own deferrals in dollars. The employer match sits outside it.
Step-by-Step Example
$80,000 salary, contributing 6%, 50% match up to 6%, $25,000 balance, 30 years, 7% return.
You contribute: 6% of 80,000 = 4,800.00 a year
Employer matches: 50% of 6% = 2,400.00 a year
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Going in: 7,200.00 a year
After 30 years: 934,895.03
Your own money: 169,000.00
Employer money: 72,000.00
Growth: 693,895.03The Number That Matters Most
Now the same person contributing 3% instead of 6%:
You contribute: 2,400.00 a year
Employer matches: 1,200.00 a year ← half of what it could be
Match left on the table: 1,200.00 a year
Compounded at 7% for 30 years: 121,997.10$121,997 forgone, for the sake of contributing three more percent of salary.
Every other number on this page is a projection resting on an assumed return. The match is certain, immediate and free. No fund choice, fee reduction or asset allocation decision available to you comes close to it.
If you take one thing from this calculator: contribute at least to the match threshold before doing anything else.
How Match Formulas Cap — Twice
"50% up to 6% of salary" catches people in both directions.
| You contribute | Employer pays |
|---|---|
| 3% | 1,200 |
| 6% | 2,400 |
| 10% | 2,400 |
| 15% | 2,400 |
Below 6% you get half of what you contributed — reduced, not forfeited entirely.
Above 6% the match stops growing. Contributing 15% earns exactly the same match as contributing 6%.
Contributing above the threshold is often still sensible for the tax treatment and the extra savings. Just do not do it expecting more match, because there is none.
The Dollar Limit Bites Too
The annual elective deferral limit caps your own contributions in dollars regardless of the percentage.
400,000 salary, contributing 20% = 80,000 intended
Capped at: 23,500For higher earners the dollar limit binds long before the percentage does, and a projection that ignores it overstates the balance considerably. The calculator says when this is happening.
Traditional or Roth?
Most explanations imply one is simply better. At the same tax rate, they are identical to the cent.
On your own contributions, over 30 years at 7% with $400 a month:
Traditional: 487,988.40 grown, less 24% tax = 370,871.18
Roth: 304.00/month after 24% tax = 370,871.18Exactly equal. Multiplication is commutative — it makes no difference whether the tax is taken before or after the growth, provided the rate is the same.
So the entire decision is a bet on your future tax rate:
- Expect a lower rate in retirement → traditional wins.
- Expect a higher rate → Roth wins.
At 24% now and 22% later, traditional is ahead by $9,759.77. At 22% now and 32% later, Roth is ahead by $48,798.84. Nothing about the accounts changed — only the rates.
Two notes on the comparison. It runs on your own contributions only: the employer match is pre-tax in both kinds of account, so including it breaks the equivalence. And it contributes the same pre-tax amount to each, which means the Roth contribution is smaller by the tax paid up front. Comparing equal nominal contributions is the usual sleight of hand, and it makes Roth look better than it is.
Understanding Your Result
Projected balance is the total at retirement.
Going in each year splits your contribution from the employer's.
The employer match is the line to act on — either confirmation you are capturing it, or the amount you are not.
Where the balance came from separates your money, the employer's, and growth. On a long horizon growth dominates both.
Worth knowing names the next thing to do: fix the match, or move on to fees.
When Should You Use This Calculator?
When you start a job. Set the contribution to at least the match threshold on day one.
When the match formula changes. Employers do change them.
Before deciding traditional or Roth. Particularly to see that the accounts are not the variable — the tax rates are.
When you get a raise. The percentage stays the same while the dollars grow; this is the cheapest time to increase the rate.
Common Mistakes
Contributing below the match threshold. The most expensive mistake available in a 401(k), and the easiest to fix.
Expecting more match above the threshold. It caps.
Ignoring the dollar limit. For higher earners it binds first.
Comparing traditional and Roth on equal nominal contributions. Compare equal pre-tax amounts.
Ignoring fees inside the plan. They come off the return every year and compound against you — the investment calculator shows what a percentage point costs over thirty years.
Cashing out when changing jobs. It triggers tax and penalties and removes the compounding, which is the only thing that made the account worth having.
Forgetting catch-up contributions. Over 50, the annual limit rises.
Every figure here is an estimate for planning. Contribution limits and tax rules change, plan terms vary, and this is not financial advice.