401(k) Growth Calculator
Project your 401(k) with contributions, employer match, raises and returns, and see exactly what a small contribution bump is worth.
How this calculator works
Each year, your contribution and your employer's match are added to your balance, then the whole balance grows at your assumed average return. Your salary (and therefore both contributions) grows every year by your assumed raise. Employer match is modeled as dollar-for-dollar up to the percentage you enter: the most common "match up to X%" plan design, though real plans vary (some match 50 cents per dollar, some use tiers).
The "+1% effect" box uses the exact numbers of your current salary to show what happens if you bumped your own contribution by one percentage point: the small per-paycheck cost after the tax break, and what that specific extra contribution grows into on its own over time.
Worked example
$50,000 salary, bumping your contribution by 1% (an extra $500/year, pre-tax): that's about $19.23 per paycheck before tax, or about $16.92 per paycheck after the tax break (at a 12% federal bracket, biweekly pay). Left to grow at 7% for 30 years, that single 1% bump alone grows to about $47,230 (from giving up less than $17 every two weeks).
Frequently asked questions
Why doesn't the 1% bump lower my FICA taxes?
A traditional 401(k) contribution is pre-tax for federal income tax, but Social Security and Medicare still apply to your full paycheck either way. Only the federal income tax portion is reduced.
What if my employer match isn't dollar-for-dollar?
Plans vary: some match 50 cents per dollar up to a cap, some match dollar-for-dollar up to a lower cap, some use tiers. Adjust the employer match field to approximate your plan, or check your plan documents for the exact formula.
Is a 7% return realistic?
7% is a commonly used long-run historical average for a diversified stock-heavy portfolio, before inflation. It's not guaranteed and real years vary widely, including negative years.
What's the 2026 contribution limit?
$24,500 for employee elective deferrals in 2026, plus an extra $8,000 catch-up if you're 50 or older ($11,250 if you're 60 to 63), per IRS Notice 2025-67. This calculator doesn't cap your inputs at that limit, so make sure your own contribution percentage stays realistic for your plan.
Does this model Roth 401(k) contributions?
No, this models traditional (pre-tax) contributions. A Roth 401(k) is funded with after-tax money, so the "+1% effect" tax-break math would not apply the same way.
Assumptions & sources
- Deposits applied at each year-end (a simplification: real per-paycheck contributions compounding throughout the year would end up slightly higher than this estimate).
- Employer match modeled as dollar-for-dollar up to the percentage you enter; real plan formulas vary.
- 2026 401(k) elective deferral limit $24,500, catch-up $8,000 (age 50+): IRS Notice 2025-67 / IR-2025-111. irs.gov
- 7% average annual return is a long-run historical assumption, not guaranteed.
Educational estimates, not financial advice.