A 401(k) and a 403(b) are both tax-advantaged workplace retirement plans, and both let employees defer part of their salary while the money grows for retirement. The practical differences are the employer you work for and the mechanics each calculator models. The 401(k) calculator projects a balance from salary deferrals, an employer match formula with a cap, monthly compounding, and an estimated retirement tax rate. The 403(b) calculator projects a balance with an annual year-by-year model that also grows salary by a raise assumption and adds employer contributions as a straight percentage of pay. Neither tool enforces contribution limits, and both are planning estimates, not guarantees.
What each calculator does
The 401(k) calculator is built around the employer-plan structure. It takes your salary, the percentage of pay you defer, the employer’s match rate and match limit, your current balance, your age and planned retirement age, an expected annual return, and a retirement tax rate. Contributions are spread into equal monthly deposits and compounded monthly. The employer match is capped: it applies the match rate to the smaller of your contribution rate and the plan’s match limit. The result shows the projected balance, monthly employee and employer contributions, investment growth, and an after-tax withdrawal estimate after applying the retirement tax rate you enter. The page notes it does not enforce IRS contribution limits, catch-up rules, or vesting schedules.
The 403(b) calculator targets nonprofit, education, church, hospital, and public-sector workers. It takes current salary, employee and employer contribution percentages, contribution start age, planned retirement age, current balance, annual return, and a salary-increase assumption. The model steps one year at a time: the existing balance grows by the annual return, that year’s employee and employer contributions are added based on that year’s salary, and salary then grows by the raise assumption. The result shows the projected balance, first-year employee and employer contributions, cumulative contributions, investment growth, final salary estimate, and contributing years. Employer contributions are a straight percentage of salary each year — there is no match cap formula — and the page notes it does not enforce IRS limits or 403(b) catch-up rules.
Side-by-side
| 401(k) calculator | 403(b) calculator | |
|---|---|---|
| Typical employer | Common in private-sector workplaces | Public schools, colleges, certain nonprofits, churches, hospitals |
| Employer contribution model | Match formula: match rate applied to the smaller of your deferral rate and the match limit | Straight percentage of salary, no cap in the model |
| Compounding | Monthly (annual contributions split into equal monthly deposits) | Annual year-by-year loop |
| Salary growth | Not modeled — salary is fixed in the projection | Explicit raise assumption grows salary each year |
| Key outputs | Projected balance, monthly employee and employer contributions, investment growth, after-tax withdrawal value | Projected balance, first-year and cumulative contributions, investment growth, final salary estimate, years contributing |
| Retirement tax treatment | Applies an entered retirement tax rate to estimate after-tax withdrawal value | Not modeled — no tax-rate input |
| Contribution limits enforced? | No | No |
When to use which
Use the 401(k) calculator when you work for a private-sector employer with a match formula and you want to see how employee deferrals and capped matching dollars combine, including what an after-tax withdrawal might look like at a retirement tax rate you enter. It is also the tool that shows how the match stops growing once your contribution rate passes the plan’s match limit.
Use the 403(b) calculator when you work for a public school, university, hospital, religious organization, or other tax-exempt employer, or when you want a projection that includes salary growth. Because it raises salary each year, it shows how raises push later contribution dollars higher — a feature the 401(k) tool does not model.
Pick the calculator that matches the plan you actually have, then check the plan documents. The two calculators also model employer money differently: the 401(k) tool caps the match with a rate-and-limit formula, while the 403(b) tool applies employer contributions as an uncapped percentage of salary. If your 403(b) actually uses a matching formula with caps, the 401(k) page’s match logic is closer to your reality, and vice versa. For broader projections, the compound interest calculator isolates pure growth, and the retirement withdrawal calculator models the spending side.
Limits and disclaimer
Both pages are educational and are not financial, tax, or legal advice. Neither calculator enforces IRS elective deferral limits, catch-up rules, or compensation limits, and neither models Roth versions, plan loans, required minimum distributions, or early-withdrawal penalties. Employer contributions in both tools may be subject to vesting — if you leave before fully vested, some matching dollars can be forfeited, and neither projection reduces the match for that risk. Contribution limits and plan rules change, so check current IRS guidance and your plan’s summary plan description before setting a deferral percentage.