ReckonBoxThe number, and whether you'll reach it
A retirement calculator answers two questions at once: how big a nest egg you need, and whether your current saving will get you there. Most tools answer one or the other, or make you piece the gap together yourself.
By the 4% rule, you need about 25 times the annual spending your savings must cover. On an $80,000 income replaced at 80%, with $24,000 from Social Security, your portfolio must supply $40,000 a year, so the number is $1,000,000 in today dollars. Saving $800 a month reaches about $578,946, a $421,054 gap that roughly $1,533 a month would close.
The gap the field leaves you to work out
The unified figure that matters is the monthly saving that closes the gap, and calculator.net and NerdWallet both leave it to the reader. calculator.net splits the question across four separate modules; NerdWallet shows a have-versus-need bar and stops.
So this tool does the whole chain in one result: the number from the 4% rule, the nest egg your plan projects to, the shortfall between them, and the exact contribution that erases it. On the default, the honest headline is not "you'll have $578,946." It is "you're $421,054 short, and $733 more a month fixes it."
Why the 4% rule sets the number
The 4% rule is a retirement guideline, from William Bengen in 1994 and confirmed by the Trinity Study in 1998, that a retiree can withdraw an inflation-adjusted 4% of the starting portfolio each year for 30 years with little risk of running out. Because 4% is one twenty-fifth, the number you need is 25 times your annual spending.
Bengen tested every 30-year retirement window in US market history back to 1926 and found no case where a 4% starting withdrawal, rising with inflation, exhausted a stock-and-bond portfolio. The Trinity professors confirmed a 95% to 100% success rate for a 50% to 75% stock mix. Lower the withdrawal rate to 3% and the number jumps to 33 times spending, which is why the rate is an input.
Where the numbers come from
The calculator works entirely in today dollars. It grows your current savings and monthly contributions to your retirement age at a real return, your expected return minus inflation, so the projected nest egg is stated in purchasing power you can recognize. The number needed is the income your savings must cover, after Social Security and any pension, divided by the withdrawal rate.
The gap is the number minus the projection, and the required contribution solves the same growth math backward, finding the monthly amount that lands exactly on the number. Everything assumes steady returns, which real markets never deliver, and it ignores the sequence of those returns, which matters most in the years right around retirement.
What this does not decide for you
This is a planning projection, not a guarantee. It does not model taxes on withdrawals, which differ sharply between a traditional 401(k) and a Roth, the sequence-of-returns risk that can sink a portfolio drawn down in a bad early decade, healthcare and long-term-care costs, or a market that simply does worse than the history the 4% rule rests on. Bengen himself has revised the safe rate up and down over the years.
None of this is advice on how much to save or how to invest it. For a plan built around your own taxes and risk tolerance, a licensed financial adviser is the right call.
Frequently asked questions
How much do I need to retire? By the 4% rule, you need about 25 times the annual spending your savings must cover. On an $80,000 income replaced at 80%, that is $64,000 a year, and with $24,000 from Social Security, your savings must supply $40,000, so the number is $1,000,000 in today dollars. A lower withdrawal rate raises the number.
What is the 4% rule? The 4% rule is a retirement guideline, from William Bengen in the Journal of Financial Planning in 1994 and confirmed by the Trinity Study in 1998, that a retiree can withdraw an inflation-adjusted 4% of the starting portfolio each year for 30 years with little risk of running out. Because 4% is one twenty-fifth, the number you need is 25 times your annual spending.
Am I saving enough for retirement? The tool projects your savings in today dollars and compares them to the number you need. On the default inputs, a plan saving $800 a month reaches about $578,946 against a $1,000,000 goal, a $421,054 gap. Raising the contribution to about $1,533 a month would close it, which is the figure most calculators leave you to work out yourself.
How is the projected nest egg calculated? The calculator grows your current savings and monthly contributions to your retirement age using a real return, your expected return minus inflation, so everything stays in today dollars. That keeps the projected nest egg and the number you need on the same scale, without a separate inflation step that can hide how much purchasing power the plan actually reaches.
How much of my income will I need in retirement? A common guideline is 70% to 80% of your pre-retirement income, since some costs like commuting and retirement saving itself fall away, while others like healthcare can rise. On an $80,000 income at 80%, that is $64,000 a year. The right figure is personal, so it is an input you can change to match your own expected spending.
Does this include Social Security? It does, as the other annual income figure, which you enter in today dollars and which lowers what your savings must provide. On the default, $24,000 of Social Security cuts the income your portfolio must cover from $64,000 to $40,000, which is why the number lands at $1,000,000 rather than $1,600,000. Estimate your benefit from your Social Security statement.