“How much will I actually need?”

Less satisfying answer first: there's no single number, and any calculator that hands you one precise figure is hiding its assumptions, not removing them.

A commonly used rough starting frame: many people aim to replace somewhere around 70–80% of their pre-retirement income each year in retirement, since some costs (commuting, saving itself) drop away while others (healthcare, time to travel) can rise. That's a starting frame to sanity-check against, not a target to chase exactly.

What actually drives the real number for you: when you plan to stop working, what you expect retirement to look like day to day, where you'll live, and what you're counting on beyond the 401(k) — Social Security, a pension, other savings. Those are personal inputs no generic rule can supply. That's the conversation worth having directly, with your real numbers on the table instead of a stranger's averages.