You can look up your expected Social Security benefits at the Social Security website. As an example, the average monthly benefit for a retiree was recently $1,229, amounting to $14,748 per year. You're likely to collect more or less than that, of course -- and you can increase your benefit by about 8% for every year that you delay taking it, beyond your normal retirement age. Also, make sure to add in income from any pensions or annuities you may have, along with dividend income and withdrawals from retirement accounts such as 401(k)s and IRAs.
and...
The $375,000 Difference
Here's some easy but important math related to your withdrawals: If you expect to have a nest egg of, say, $1 million, multiply it by 0.04 -- which is 4% -- to see what your initial withdrawal will be. In this case, it's $40,000. If you manage to amass $300,000 by retirement, a 4% withdrawal will net you $12,000 in your first year.
You can flip those numbers around, too. If your calculations show that you'll need an annual income of about $50,000 in retirement, multiply that by 25 to see how big a nest egg you'll need to generate $50,000 via a 4% withdrawal rate: $1.25 million.
Of course, your other income sources can reduce that. If you're expecting $15,000 in Social Security income and $10,000 in pension income, then your savings and investments will only need to generate $25,000 in your first year. Multiply that by 25, and you'll arrive at a nest egg of $625,000.
That's a great illustration of why you may not need to accumulate $1 million for your retirement.