What I haven’t seen yet, on a quick read-through of the thread:
Let’s say you are going to retire at age 63, but put off taking your SS until you hit 65 or whatever.
In the intervening years, you have to rely on your 401(k) / IRA / whatever to make up the income you’d have been getting from SS.
That means you’re drawing down on your principal… thereby reducing how long that money would last.
I’ve read that to make your retirement money last long enough, it’s recommended that you take only about 4% of your money each year. So if you have a million dollars in an IRA, you’re taking 40,000 per year.
If, at age 65, you’d get 3,000 a month (36,000 a year) from Social Security, you’re going to be getting 76,000 a year. If you need that 72,000 a year starting at 63, you will be taking all 76,000 (152,000 total) from your IRA.
So (ignoring any growth in the IRA in the meantime), you now hit age 65 with 848,000 in your IRA. That 4% is 36,400 now (1,000,000 - 152,000 = 848,000, and 4% of that is 33,920 if I’ve done my math right). So your income is 69,920. To bring it up to 76,000 a year, you’d need to draw down a little more than 4 percent.
A more precise picture there would take into account assumed growth in the IRA (e.g. that 1 million IRA is going to be worth more than 848,000 after 2 years, even with taking 76K a year).