To start withdrawing 4% of your portfolio while maintaining your desired spending level, you need to accumulate 100/4 or 25 times that annual spending number.
A 4% withdrawal rate is going to be safe in most circumstances, but a withdrawal rate closer to 3% is more bulletproof. Saving up 30x to 35x your anticipated retirement spending can go a long way towards ensuring your money will outlast you.
Work a few more years after achieving financial independence and you’ll likely find yourself with an initial withdrawal rate of less than 3%. You don’t even have to work that hard to make it happen.