How much do you actually need to retire?

A common way to size a retirement corpus is to assume it needs to last forever — withdraw a small enough percentage each year, the thinking goes, and the principal never runs out. That’s a reasonable approach for early retirement, where the horizon really could stretch for many decades. For a conventional retirement age with a specific, estimable number of years ahead, it’s usually more corpus than you actually need.

Your corpus only needs to last as long as you do

If you can reasonably estimate how many years you’ll spend in retirement — life expectancy minus retirement age — you can size a corpus specifically for that stretch instead of forever. Withdrawals still grow with inflation every year, and the remaining balance keeps earning a return, but the corpus is allowed to run down to zero right around when you expect to no longer need it, rather than staying intact indefinitely.

How much smaller a finite corpus really is

What drives the number more than anything else

The length of your expected retirement is the single biggest lever on this calculation — retiring a few years later, or planning for a shorter retirement, shrinks the required corpus noticeably, since it directly changes how many years of withdrawals the corpus has to cover. Life expectancy is a genuine unknown, though, which is why it’s worth erring toward planning for a longer retirement than you expect rather than a shorter one: running out of corpus late in life is a far worse outcome than having some left over.