What the retirement number actually represents
Your retirement number is the price of an income stream. It is not a savings goal picked from a magazine; it is the present value, on the day you stop working, of every withdrawal your portfolio has to make for the rest of your life. Price that stream and you have the target. Everything else — the multiple of salary, the round million, the 25-times rule — is a shortcut to the same present value under particular assumptions.
Three quantities drive it. The first is the spending your portfolio has to cover, which is your total spending minus everything guaranteed: Social Security, a defined-benefit pension, an annuity, rental income you consider reliable. Guaranteed income is enormously powerful here because it shrinks the numerator directly. A household spending $70,000 with $30,000 of Social Security needs a portfolio for $40,000, not for $70,000, and the target falls by well over half.
The second is how long the money must last, which is a planning choice rather than a forecast. Planning to your life expectancy means running out of money in about half of all outcomes. The third is the real return — what the portfolio earns after inflation. Nominal returns are irrelevant to this calculation because your spending inflates alongside them, which is why the formula divides one by the other rather than subtracting.
The formula and why it has this shape
The target is a first-year withdrawal multiplied by an annuity factor. The annuity factor answers a single question: how many dollars of capital does it take today to fund one dollar a year, rising with inflation, for n years? That is the standard present-value-of-an-annuity expression, evaluated at the real rate.
Start with the real return. If your portfolio earns 5% while prices rise 2.5%, you have not gained 2.5%; you have gained (1.05 ÷ 1.025) − 1 = 2.439%. The subtraction shortcut is close enough at low rates and visibly wrong at high ones, so this calculator uses the exact form. Once you work at the real rate, an inflation-indexed withdrawal becomes a level withdrawal, and the whole inflation problem disappears from the annuity.
The factor itself, [1 − (1 + i)−n] ÷ i, is the sum of n discounted dollars. Multiplying by (1 + i) shifts every payment one year earlier, which is what happens when you withdraw at the start of each year instead of the end. That timing choice moves the target by roughly the real rate — small, but real. When the real return is zero the factor is exactly n: with no growth, funding thirty years of spending takes thirty years of spending, and that identity is a good sanity check on any retirement calculator.
Finally, inflation between now and retirement. Your spending is entered in today's dollars, so it must be inflated by (1 + π)t to reach the dollars of your retirement year. That is why the answer looks large for someone twenty years out. Dividing it back gives the target in today's purchasing power, and the two numbers describe the same plan. Use the compound interest calculator if you want to see that growth factor on its own.
Worked example: retiring in 10 years on $60,000 with a $20,000 pension
You spend $60,000 a year today and expect $20,000 of guaranteed income. You retire in 10 years and want the money to last 20 years, withdrawing at the start of each year. You assume 3% inflation and a 3% return during retirement.
- Net the spending. $60,000 − $20,000 = $40,000 a year, in today's dollars.
- Inflate to the retirement year. (1.03)10 = 1.343916, so the first-year withdrawal is $40,000 × 1.343916 = $53,756.66.
- Find the real return. (1.03 ÷ 1.03) − 1 = 0. The portfolio grows exactly in line with prices, so it gains nothing in purchasing power.
- Take the annuity factor. At a zero real rate the factor is simply the number of years: 20.
- Multiply. $53,756.66 × 20 = $1,075,133 on the day you retire.
- Translate back. $1,075,133 ÷ 1.343916 = $800,000 in today's money, which is exactly $40,000 × 20 — the same plan seen from today.
Now raise the retirement return to 5% and leave inflation at 3%. The real rate becomes (1.05 ÷ 1.03) − 1 = 1.942%, the twenty-year annuity-due factor falls to 16.76, and the target drops to about $901,100. Two percentage points of assumed return cut the requirement by roughly 16%, which tells you how much of any retirement number is assumption rather than arithmetic.
How many years of spending you need, by horizon and real return
| Years | 0% real | 1% real | 2% real | 3% real | 4% real | 5% real |
|---|---|---|---|---|---|---|
| 20 | 20.00 | 18.23 | 16.68 | 15.32 | 14.13 | 13.09 |
| 25 | 25.00 | 22.24 | 19.91 | 17.94 | 16.25 | 14.80 |
| 30 | 30.00 | 26.07 | 22.84 | 20.19 | 17.98 | 16.14 |
| 35 | 35.00 | 29.70 | 25.50 | 22.13 | 19.41 | 17.19 |
| 40 | 40.00 | 33.16 | 27.90 | 23.81 | 20.58 | 18.02 |
The 25× multiple behind the 4% rule sits between the 1% and 2% columns at 30 years, and exactly on the 0% column at 25 years — a 30-year annuity-due costs 25 times its first payment at a real return of about 1.3%.
How to read your target
Look at the multiple before you look at the dollars. The multiple is the annuity factor, and it tells you how many years of spending the target represents. A multiple near 25 puts you in the same territory as the 4% rule. A multiple above 30 means you have combined a long horizon with a low real return, and the plan is leaning heavily on capital rather than returns. A multiple under 15 means either a short horizon or an optimistic real return, and it deserves a second look.
Compare the annuity answer with the shortcut answer. They differ for a reason: the annuity formula assumes you spend the portfolio down to zero over a fixed horizon, while a fixed withdrawal rate like 4% is calibrated to survive bad market sequences over about thirty years and usually leaves money behind. If your annuity target is far below the shortcut target, you are relying on average returns arriving in a friendly order, which is the assumption that sequence-of-returns risk attacks. The safe withdrawal rate calculator works the same problem from the other end.
Then read the gap. A shortfall is a statement about four levers, not one: save more, work longer, spend less, or claim more guaranteed income. Each year of extra work is unusually powerful because it adds a year of contributions, adds a year of compounding, and removes a year from the withdrawal horizon at the same time. If your projected savings already exceed the target, the surplus is your margin against a bad decade, not spare cash.
Assumptions and limits you should know about
- Returns are assumed smooth. The formula applies the same real return every year. Real markets do not, and a bad first decade damages a portfolio in drawdown far more than the same decade later. Treat this as a target, not a guarantee.
- Spending is assumed constant in real terms. Actual retirement spending often falls in the middle years and rises again with health costs, and this calculator cannot model that shape.
- Taxes are inside your spending figure, not modelled separately. A dollar from a traditional 401(k) is worth less than a dollar from a Roth, so the same target funds different lifestyles depending on which accounts hold it.
- Guaranteed income is assumed to be inflation-indexed. Social Security is; most private pensions are not. If yours is a level pension, its purchasing power will decline, so enter a lower figure than the current payment.
- Health care before Medicare is easy to underestimate. Retiring at 60 means five years of premiums that a 65-year-old never pays.
- The horizon is not your life expectancy. Plan past it. For a 65-year-old couple, the chance that at least one is alive at 90 is substantial, so 30 years is a floor rather than a conservative choice.
Where this sits among the other retirement calculations
This calculator answers the accumulation question: how big must the pile be. Three other calculations answer the questions on either side of it.
Before retirement, the question is whether your contributions get you there. The gap figure here converts to a level annual saving using the sinking-fund factor, but real contributions rise with pay and employer matching complicates the picture; a monthly investment for a goal calculation handles that directly. If you are chasing early retirement, the FIRE number calculator is the same present-value logic with a longer horizon and a lower withdrawal rate.
After retirement, the question flips: given the pile you actually have, how long does it last and how much can you take? That is the portfolio longevity calculation, which solves the same equation for n instead of for the present value. And once you reach 73 or 75, the IRS imposes its own minimum on top of your plan, which the RMD calculator computes.
One structural alternative is worth naming. If you want a genuinely guaranteed inflation-indexed income rather than a portfolio that probably works, you can buy one: a ladder of Treasury Inflation-Protected Securities, or an inflation-adjusted single premium immediate annuity. Both are priced by exactly the annuity formula on this page, at whatever real yield the market offers, which is why comparing your assumed real return against the current TIPS yield is a fast reality check on the whole plan.