The safe withdrawal rate (SWR) method is one that retirees use to determine how much they can withdraw from their accounts each year without running out of money before reaching the end of their lives. The safe withdrawal rate method is a conservative approach that tries to balance having enough money to live comfortably with not depleting retirement savings prematurely.
The first study come from financial planner William Bengen. Essentially, Bengen tested a variety of withdrawal rates using historical rates of returns for stocks and bonds. He found that 4% was the highest withdrawal rate retirees could use if they wanted their money to last at least 30 years, assuming they invested at least 50% of their savings in stocks. The 4% rule quickly became the default withdrawal rate for retirees who wanted to make sure that their retirement nest egg would be around as long as they were.
But today what withdrawal rate can be reasonable? I tried to give an answer looking at this site
You can simulate the expected real return of different asset in next 10 years
As you can see there isn’t an asset with expected return above 6%. But if you change from expected to historical data expected return are much higher
So with 4% today probably is unrealistic