401k Calculator

Written by Great Medico

Updated September 25, 2026 •3 min read

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401k Calculator is useful when you want a quick number without losing sight of the assumptions behind it. It projects how a retirement balance may grow from the current balance, annual contributions, return assumption, and annual fee shown.

What this calculator does

401k Calculator projects how a retirement balance may grow from the current balance, annual contributions, return assumption, and annual fee shown. The visible form contains Current retirement balance, Your annual contribution, Employer match rate, Maximum annual employer match, Expected annual return, Annual account fee, Years until retirement, Annual 401(k) contribution limit. These are the inputs that define this calculator’s scope. If a value, rule, or adjustment is not represented by a working field, it should not be assumed to be included in the result.

How to use it

Enter Current retirement balance, Your annual contribution, Employer match rate, Maximum annual employer match, Expected annual return, then complete the remaining displayed fields: Annual account fee, Years until retirement, Annual 401(k) contribution limit. Enter percentage or rate fields on the scale shown by the form rather than converting them to decimals yourself. Keep monetary inputs in the same currency, or use the currency selector when one is provided. Keep time and payment-frequency assumptions consistent with the labels on the page. Before calculating, recheck Current retirement balance and the other values that materially affect the result. For a clean comparison, hold the other inputs constant while changing one assumption at a time so you can see what is driving the result.

How the calculation works

The calculator uses a monthly net rate based on expected annual return minus annual account fee. It adds monthly contributions, plus any modeled employer match where those fields exist, and compounds the balance over the entered years. This is the calculation method that should anchor any manual check of the output. If a displayed field does not affect the current calculation, that limitation is stated below rather than silently treating the field as part of the formula.

Example

With the displayed example values (Current retirement balance = 50,000, Your annual contribution = 7,000, Employer match rate = 50, and Maximum annual employer match = 3,000) and the remaining defaults unchanged, the current calculator returns $893,037.14 for projected retirement balance. Replacing those defaults with your own values recalculates the same relationship; change one input at a time if you want to see which assumption is driving the difference.

How to interpret the result

The result is a scenario projection rather than a promise. More time, larger contributions, or a higher assumed net return increase the modeled ending balance; higher fees reduce it. Compare results produced from the same definitions and time period. A mathematically larger or smaller number is not automatically better unless the financial context makes that direction meaningful.

Limitations and notes

The visible annual 401(k) contribution-limit field is not enforced by the current calculator. For 2026, the IRS employee elective-deferral limit is $24,500, while the form default is $23,000; plan-specific catch-up and employer contribution rules also apply. Enter only a contribution level you have independently confirmed is allowed. Where the calculator depends on estimates, rates, accounting classifications, or future behavior, test more than one plausible scenario before making a decision.