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:
- 📈 Projected yearly return rate
- 🛍️ Monthly withdrawal sum
- 💰 How much money you have
They are all equally important aspects.
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.
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?"