How much money do I need to retire?

Generally, it is recommended to use 4% initial withdrawal. That gives you a 99% chance to make it through 30 years, using up the capital in the process. So unless you plan to die in 30 years, that's too thin.
The 4% rule gives you however a nearly as good chance to still have the capital or even more, so if you're fine with maybe 98.5%, it could work - nobody knows if the financial market future will really look similar to the past.

I'd like to know how you pay health insurance from that amount? Which country are you in? For these amounts, in the US you can only afford a 'go-to-church-and-pray-for-the-best' type insurance. Note also that health care cost overall is expected to increase faster than inflation, and in addition increases with age, so you'll get a double dip in increased cost.
You might want to plan for 3.5% or even 3% to be more secured.

Otherwise, your calculation is correctly executed.

This suggestion will probably engender some hisses and downvotes but a variable annuity would do the trick.

I don't know what current guaranteed deferred rates are (I've had one as high as 10% simple) but about $100k in one with a 6% deferred growth benefit would grow to $250k in 25 years (age 60), at which time you could withdraw 6% or $15k a year until the day you die.

On the growth side, the $100k would be invested in the market (sub accounts). If it grew at a higher rate than the guaranteed 6% deferred side, you'd end up with a larger pool of money ( > $250k) from which to draw on at age 60 and you'd get more than $15k per year until you die (6% of that larger amount). If you did not live many years past age 60, your estate would get this larger amount less any withdrawals made.

Understand that due to high annuity commissions, you'd do a lot better in the market if the market rose more than 6% a year but you wouldn't have the guaranteed payments for life that the annuity would provide.

Given what $15k pays for now (in the U.S) and what it will be able to pay for in 30 years or more, I wonder how you will be able to survive on $15k in future dollars unless you live in a 3rd world country.

If you have a monthly budget, push it forward 30 years based on estimated inflation, adjusting for things like a paid-off mortgage, health insurance costs growing much faster than inflation, not contributing to 401(k)/IRA anymore, SS income (or lack thereof), etc. That'll give you a very rough estimate of how much you need each month in retirement. (Update it every couple of years, since "life happens".)

Then push forward your investments, and 401(k)/IRA contributions at the growth rate of your choice.

Lastly, compare the two numbers...

But not really lastly, because spreadsheets are so flexible at letting you adjust the yearly draw-down for inflation, retiring at different ages, deciding whether your investments will grow slower during retirement, etc, etc, etc.

I've created future-fortune.com just for that, which is a very basic investment calculator which aims to vastly simplify planning for retirement.

How much money you need is only one part out of three:

1. ? Projected yearly return rate
2. ?️ Monthly withdrawal sum
3. ? How much money you have

They are all equally important aspects.

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The first one, Projected yearly return rate is dictated by your investing skills (luck).
Some make 4-6%, some 10% some 20% or above. This is a skill you should constantly work on.

The second one, Monthly withdrawal sum is dictated by your living standards. you can live with your parents, forever, eat their food, pay no bills and basically have almost zero expenses, or you can own a house, 3 children and a mortgage...your life choices are up to you. This should be lowered to the minimum possible that will not harm your levels of happiness drastically.

The third, How much money you have is your starting point, it can be money from work, inheritance, whatever. You can retire but still "work" a few hours here and there, or you choose never to work again, living off your investments portfolio.

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I suggest: finding the highest paying job you can and stick to it until you can no longer stand it, or earned "enough".

Hone your investments skills, but do not be lured into "gambling"-style investments such as bitcoin or stock options. Stick to what's safe. Slowly gathering gains is what I advise. keep the greediness as low as you can.

Lastly, try to never buy anything without asking yourself "do I really really need this?"