b2KIT

401(k) Contribution Optimizer

Optimize 401(k) contributions with employer match analysis, Roth vs Traditional comparison, and tax-deferred growth projection.

Tested tool guide Tested browser tools Checked August 15, 2026

What 401(k) Contribution Optimizer does, with a checked example

This tool models a 401(k) contribution strategy from three angles: how much of your employer's match you're actually capturing, whether Roth or Traditional treatment leaves you better off, and what the balance could grow to by retirement under a chosen return rate. You enter salary, contribution rate, the plan's match formula, and a tax assumption; it splits out employee vs employer dollars and compounds them forward. One thing the match-capture check makes visible: contributing below the match threshold leaves free employer money on the table, and the Roth/Traditional comparison is only as good as your guess about your tax bracket in retirement.

Worked example

A concrete input and expected output from the current implementation.

Input

Salary: $80,000; contribution rate: 6%; employer match: 50% up to 6% of salary

Expected output

Employee contribution: $4,800/year; employer match: $2,400/year; combined total: $7,200/year (9% of salary)

6% of $80,000 is $4,800, and a 50% match on that amount adds $2,400, so the two together equal $7,200, or 9% of salary.

How the result is produced

1

Match capture calculation

The tool applies the plan's match formula (e.g., 50% up to 6% of salary) to your entered contribution rate, computing employee and employer dollars separately. If your rate sits below the threshold needed to trigger the full match, it flags the shortfall so you can see exactly how many match dollars you're forfeiting at your current rate.

2

Roth vs Traditional projection

Traditional contributions are treated as pre-tax, reducing current taxable income at your entered marginal rate; Roth contributions are treated as post-tax with tax-free qualified withdrawals. Both paths are compounded at your chosen annual return rate to a target retirement age, so you can compare projected balances and take-home-pay impact side by side.

Good uses

  • checking whether your current contribution percentage captures the full employer match before increasing or decreasing it
  • weighing a switch from Traditional to Roth, or a split between the two, based on projected balances under different tax-rate assumptions
  • projecting how a 401(k) balance grows over a chosen number of years at a given contribution rate and return assumption

Limits and checks

  • The growth projection assumes a constant annual return, salary, and contribution rate every year - it won't reflect market volatility, raises, or mid-year contribution changes
  • The Roth vs Traditional comparison depends on both your current tax rate and your assumed future tax rate; the 'better' option only flips if that assumption crosses the strategy's break-even point, not with any error in your guess
  • It won't automatically apply the current-year IRS elective deferral limit or catch-up contribution rules unless you enter them yourself, so results above the real cap aren't valid

Common questions

Does it use the current IRS contribution limit automatically?

Not necessarily - confirm this against the current-year IRS elective deferral limit before relying on the output, since annual limits and catch-up amounts change and the tool depends on what you enter for salary and contribution rate.

Does it account for employer match vesting schedules?

No. It treats employer match dollars as fully yours once contributed. If your plan vests match funds over several years, the projected balance overstates what you'd actually keep if you left the job before fully vesting.

References and verification

The example and behavioral notes were checked against the browser implementation. Standards and primary references below define the relevant format, formula, or platform behavior.

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