Retiring at 55 is very doable, but it's a different game from finishing at 67 — you've got 35+ years to fund and, for the first decade, no state pension or Medicare to lean on (which is exactly the stretch most calculators skip over). This one doesn't: put in your age, what you've saved so far and your target, and it shows what an early finish line actually looks like for your numbers.
The thing to watch isn't just "have I got enough" — it's the first few years. A rough market run right after you stop working does far more damage at 55 than the same run at 70, simply because the money has to last so much longer (sequence-of-returns risk, if you want the textbook name). Try it with your real figures, then pull the retirement age back a year or two and watch how much difference a little more runway makes.