How to use the retirement calculator
The Will I have enough? tab projects your savings to retirement and tests them against your spending. The Earliest retirement age tab uses the same inputs and searches for the youngest age at which the plan works. Enter every money amount in today’s dollars; the calculator applies inflation for you.
- Ages. Your current age, the age you want to retire and the age the money must last to. Planning to 95 rather than to an average life expectancy protects against the real chance of living longer than average.
- Savings and contributions. Your current retirement balance across 401(k), IRA and other accounts, what you add each month including any employer match, and how fast you expect to raise that amount. In the US the 2026 limit on employee 401(k) deferrals is $24,500, and on IRA contributions $7,500, before catch-up amounts for people aged 50 and over.
- Returns and inflation. One average return for the saving years, another for retirement, and an inflation rate that raises your spending each year.
- Retirement income. What you want to spend per year in today’s dollars, plus Social Security or pension income and the age it starts. Your Social Security statement gives an estimate for each claiming age.
The results show the surplus or shortfall, both sides of the comparison, the extra monthly saving needed and the age the money runs out. The chart follows the balance through your whole life, and the table gives every year.
How the calculation works
While you work, contributions go in at the end of each month and the balance compounds monthly at the equivalent of the annual return. The monthly amount rises once a year by the contribution growth rate.
i = (1 + r1)1/12 − 1BR is the balance at retirement, S today's savings, n the years until retirement, c the monthly contribution, g its yearly growth, r1 the return before retirement and i the matching monthly rate.
In retirement, one withdrawal at the start of each year covers spending minus other income, raised with inflation from today. The nest egg needed is the present value of those withdrawals at the retirement return:
Nest egg = Σt=0..T−1 Wt ÷ (1 + r2)t
Today's dollars = future dollars ÷ (1 + π)nD is the desired income and Ot other income in year t of retirement (both in today's dollars), π inflation, r2 the return in retirement and T the years from retirement to the plan-to age.
The gap is the projected balance minus the nest egg. If it is negative, the extra monthly saving is the gap divided by what $1 a month, rising with your contributions, would grow to by retirement.
A worked example
You are 40 with $150,000 saved, and you put in $1,000 a month, raising it 2% a year. You expect 6% a year until you retire at 65, 5% after that, and 2.5% inflation.
By 65 the balance reaches $1,460,803, which is $787,943 in today’s dollars. You will have contributed $384,364 of it yourself.
You want $60,000 a year in today’s money and expect $24,000 from Social Security from age 67. Funding that to age 95 needs a nest egg of $825,610 in today’s dollars ($1,530,635 at the time).
The result is a shortfall of $37,667 in today’s dollars. Left alone, the money runs out at age 92. Saving an extra $85 a month from now closes the gap. On the second tab, the earliest age that works with your current saving is age 66.
Reading the results
The gap is the headline. It compares two large numbers that both rest on assumptions, so treat a small surplus or shortfall as “about on track” rather than as a precise verdict. A gap of a few percent of the nest egg can change sign with a half-point change in returns.
Today’s dollars are the ones to judge. Future balances look impressive because they include decades of inflation. The future-dollar figures still matter: they are what your statements will show, and the first-year withdrawal of $111,237 in the example is the cash you would take out in the year you retire.
The run-out age is a warning, not a forecast. It assumes the same return every year. Real markets vary, and a bad stretch early in retirement shortens the timeline even if the average holds. The retirement Monte Carlo calculator tests the plan across thousands of return paths.
What changes the answer most
| Change from the example | Surplus or shortfall (today’s $) | Money runs out |
|---|---|---|
| The example | -$37,667 | Age 92 |
| Retire at 67 instead of 65 | $122,320 | Past age 95 |
| Save $1,500 a month | $182,681 | Past age 95 |
| Spend $50,000 a year | $178,495 | Past age 95 |
| Return before retirement 5% | -$166,413 | Age 86 |
| Inflation 3.5% | -$312,962 | Age 82 |
Retiring later works twice over: it adds years of saving and growth, and it removes years of withdrawals, including the expensive years before Social Security starts. Spending is the other strong lever, because it sets the size of every withdrawal for decades. A lower return before retirement hurts more than most people expect, because it compounds over the whole saving period. Higher inflation does the most damage in the table: with the same returns, it lowers the real return in both phases and raises every withdrawal.
Finding the earliest retirement age
The second tab repeats the calculation for every possible retirement age, from now to the year before the plan-to age, and picks the first one at which projected savings cover the nest egg. With the example inputs that is age 66. Saving $1,500 a month brings it forward to 63, and cutting spending to $50,000 a year instead has the same effect.
The chart on that tab shows why the search works: projected savings rise with each extra working year, while the nest egg needed falls because there are fewer years to fund. Where the two lines cross is the earliest age. Retiring right at the crossing leaves no margin, so many planners add a few years or a spending cushion on top. For an aggressive early-retirement target, the FIRE calculator frames the same question around a savings rate.
What this calculator does not include
- Taxes. Withdrawals from traditional 401(k)s and IRAs are taxable income in the US; Roth withdrawals generally are not. Enter spending that includes the tax you expect to pay.
- Variable returns. One steady return hides sequence-of-returns risk. See the retirement withdrawal calculator for how the order of returns changes the outcome.
- Non-indexed pensions. Other income rises with inflation here, which suits Social Security. Many private pensions are fixed in dollars and lose buying power over time.
- Changing spending. Spending often falls in later retirement while healthcare costs rise. The retirement income calculator projects healthcare separately.
- Required minimum distributions, early-withdrawal penalties, one-off costs and any money left to heirs. For a simple drawdown of a fixed balance, the how long will my money last calculator works month by month.