A 401(k) and a 529 are both tax-advantaged savings vehicles, but they answer different questions for different goals. The 401(k) calculator projects how salary deferrals, employer match dollars, and tax-deferred growth build a retirement balance by a target age, then estimates its after-tax withdrawal value. The 529 calculator starts from the spending side: it inflates future education costs and works backward to the monthly contribution needed to cover them. The difference in direction matters — one tool reports a balance, the other reports a required savings rate.
What each calculator does
The 401(k) calculator models a traditional workplace 401(k). You enter salary, your deferral percentage, the employer’s match rate and match limit, current balance, age and planned retirement age, expected annual return, and a retirement tax rate. Contributions become equal monthly deposits and compound monthly. The match is capped at the smaller of your contribution rate and the match limit, so the employer adds match-rate dollars only on eligible deferrals. Outputs include the projected balance, monthly employee and employer contributions, investment growth, and an estimated after-tax withdrawal value after applying the retirement tax rate. The page does not enforce IRS contribution limits or model Roth 401(k) contributions.
The 529 calculator estimates education costs and a savings target. You enter the beneficiary’s current age, the age school starts, the number of school years, today’s annual cost, expected education cost inflation, any initial investment, and an assumed annual return. It inflates each school year’s cost separately, estimates a monthly contribution for each year, and sums them into one required monthly contribution. Outputs include the future education cost, required monthly contribution, annual contribution, years until the first school year, deposit years, and first- and final-year estimated costs. The page is explicit that qualified 529 withdrawals are generally free from federal income tax, and that its simplified model can over-credit a starting balance across multiple school years.
Side-by-side
| 401(k) calculator | 529 calculator | |
|---|---|---|
| Goal modeled | Retirement balance | Education costs and the savings rate to cover them |
| Primary output | Projected balance at retirement | Future education cost and required monthly contribution |
| Key inputs | Salary, deferral %, employer match rate and limit, current balance, ages, return, retirement tax rate | Beneficiary age, school start age, school years, today’s cost, cost inflation, initial investment, return |
| Employer money | Employer match with rate and cap | None |
| Direction | Projects forward to a balance | Works backward to a required contribution |
| Compounding | Monthly, contributions split into equal monthly deposits | Monthly (annual return divided by 12) |
| Tax frame | Pre-tax contributions in, withdrawals taxed at the entered rate | After-tax contributions, qualified withdrawals generally federal-tax-free |
| Contribution limits enforced? | No | No |
When to use which
Use the 401(k) calculator when the question is retirement: how much a workplace plan with salary deferrals and matching dollars might hold by a target age, and what an after-tax withdrawal could look like. It is the tool that shows how employer match dollars compound alongside your own deferrals, and how the match stops growing once your deferral rate exceeds the match limit.
Use the 529 calculator when the question is education: how much a specific school path may cost in future dollars, and what monthly contribution closes the gap given an existing balance. It is built around a beneficiary’s school timeline, so it handles different start ages and the number of years to fund — things a retirement projection ignores.
The two goals are not either-or. Many households save for both at once, and the tools can be used side by side: run the 401(k) page to sanity-check that retirement contributions stay on track, and the 529 page to set an education savings rate that fits the same budget. The budget calculator can help find the tradeoff that funds both, and the compound interest calculator isolates the pure growth assumption behind either projection.
Limits and disclaimer
Both pages are educational and are not financial, tax, or legal advice. Neither enforces IRS contribution limits, and both depend on return assumptions the user chooses — real portfolios do not earn a steady monthly return. The 401(k) page does not model Roth contributions, loans, early-withdrawal penalties, or vesting, and its after-tax figure only applies the tax rate you enter. The 529 page depends on a cost-inflation assumption, varies by state plan rules, and uses a simplified model that can over-credit a starting balance across school years. Contribution limits, plan rules, and state 529 terms change, so verify current guidance and plan documents before acting on any number.