How Much Do You Actually Need to Retire? Start With the Gap
The retirement question is not “what will I have.” It is “what must the portfolio still cover after the checks that do not care about the S&P 500.” Start there, and the rest of the math gets honest fast.
Start with the gap, not the pile
Most retirement calculators ask about your investments first. That is backwards. The checks that arrive no matter what the market does — Social Security, a pension — do the heavy lifting in almost every plan. The portfolio only has to cover what is left. So the honest inputs are simple:
- Need per month in retirement, in today's dollars.
- Social Security per month, in today's dollars.
- Pension per month, in today's dollars.
- Current investments, years until retirement, and the monthly amount you will keep investing.
- Expected return, inflation, and withdrawal rate — the Planner defaults to 7 percent, 3 percent, and 4 percent.
The five lines that matter
From those inputs, five numbers tell the story:
- Income gap today = need minus Social Security minus pension.
- Income gap at retirement = that gap grown by inflation for the years remaining.
- Nest egg needed = the annual gap at retirement divided by the withdrawal rate.
- Projected nest egg = current investments grown monthly, plus monthly contributions.
- Savings gap = needed minus projected. This is the number you are actually trying to close.
A worked example
Take a $6,000 monthly need, $2,200 in Social Security, and no pension. That is a $3,800 monthly gap today. At 3 percent inflation over 10 years, the gap becomes about $5,100 a month in future dollars — roughly $61,200 a year. At a 4 percent withdrawal rate, the nest egg needed is about $1.53 million. Change the withdrawal box to 3.5 percent and the same gap needs about $1.75 million.
That last move is the whole point of the withdrawal-rate box: it is doing sensitivity analysis for you. It is not promising the market will cooperate — it is showing how much the answer moves when your assumptions do.
What one guaranteed dollar is worth
Here is a trick for appreciating Social Security. At a 4 percent withdrawal rate, every $1 a month of guaranteed income replaces about $300 of nest egg: $1 a month is $12 a year, and $12 divided by 0.04 is $300. So a $2,200 monthly Social Security check does the work of roughly $660,000 in the portfolio — money you do not have to save, and that never faces sequence risk. That is why the gap, not the pile, is the question: guaranteed income is the cheapest retirement funding there is.
Three levers when the gap is too big
If the savings gap comes back red, you have three honest levers — the same ones the Planner points to. Invest more each month. Retire later, which adds compounding years and subtracts funded years. Or need less per month. What does not work: raising the expected-return box until the gap disappears. That is decorating, not planning.
What the gap does not include
The gap math above is pre-tax and pre-healthcare. Taxes take a cut of withdrawals, and the health line — premiums, IRMAA surcharges, the long-term-care risk — belongs inside “need per month,” not next to it. The healthcare article walks through those bills; the honest version of this exercise adds them to the need number and reruns the gap.