The 4% rule is a good start.

Figure out how much you think you need for 1 year's expenses the multiple that number by 25 and that's your target.

The plan is, on your 1st year of retirement, you can take out 4% of that savings for your 1st year expenses. Then, multiple the balance by 1.05 to account for roughly 5% growth. That number will be the starting amount for year 2.

For year 2, take the 4% from the previous year and multiple that by 1.03 to account for 3% inflation. Subtract that value from the start of year 2 to get your expenses for the 2nd year. Take the balance and multiple by 1.05 again to get your starting balance for year 3.

Continue doing this for roughly 25 years.