A 401k calculator projects what your workplace retirement account will be worth by the time you retire. You enter your age, salary, current balance, how much you contribute, your employer's match and an expected return — and it compounds every future contribution to a single number: your balance at retirement.
The reason it matters is that retirement saving is driven by compounding, which is almost impossible to estimate in your head. Small changes — one extra percent of pay, a few more years, capturing the full employer match — can swing the outcome by hundreds of thousands of dollars. Seeing that live, as you move a slider, is what turns an abstract goal into a concrete plan.
This is the pillar tool. Alongside it are focused calculators for the employer match, early-withdrawal penalties, Roth vs traditional, paycheck impact, required minimum distributions and more — each solving one part of the 401k question in full.