How a 401(k) grows
Three forces build your balance: your contributions, your employer’s match (free money — always contribute at least enough to get the full match) and compound growth on everything already invested. Over decades, growth usually becomes the largest of the three.
2025 contribution limits
The employee elective deferral limit is $23,500 for 2025 (plus a $7,500 catch-up at age 50+). Employer match doesn’t count toward that employee limit. This calculator caps your own contribution at $23,500.
The match is the headline
A common formula is “100% match up to 6% of pay”. Contributing less than the match limit leaves guaranteed money on the table — it’s an instant 100% return before any market growth.
Frequently asked questions
Does this include the employer match?
Yes. Set the match percentage and the salary limit it applies to (e.g. 100% up to 6%). The match is added to your own contribution each year.
What return should I assume?
A long-run diversified stock/bond portfolio has historically returned around 6–8% before inflation. Use a conservative figure and treat the result as a range.
Is my contribution capped?
Yes — at the 2025 employee limit of $23,500 (under age 50). Employer match is on top of that and isn’t limited by the same cap.