What the retirement savings calculator does
This retirement savings calculator projects how much you’re likely to have saved by the time you retire, based on what you already have, what you add every month, and the return you expect. Enter your current age, your target retirement age, your current balance, your monthly contribution and an expected annual return, and it shows your projected capital instantly — both in nominal terms (actual currency units in the year you retire) and in today’s money, adjusted for inflation.
This is not a calculator of your state pension. It doesn’t estimate what Social Security, ZUS, the Seguridad Social or any other public pension system will pay you based on your contribution history — that’s a separate, country-specific question governed by pension law, and it changes with legislation. This calculator answers a different question: given the assumptions you enter, how much will your own private savings and investments be worth — and, if you set an income goal, how much you need to put aside each month to get there.
Optionally, set a retirement income goal — either a target monthly income or a percentage of your current income to replace — and the calculator works out the capital you’d need using two well-known methods (more on that below), plus the monthly contribution required to close any gap.
How to use the retirement savings calculator
- Current age and retirement age. These define your saving horizon in years. The default retirement age is 65 — change it to match your own plan.
- Current retirement savings. Whatever you already have set aside for retirement — a brokerage account, a pension fund, savings earmarked specifically for later.
- Monthly contribution and expected annual return — a nominal rate before inflation, e.g. a long-run average stock market return.
- Advanced options, if you open them:
- Inflation — used to convert your projected nominal capital into today’s purchasing power (default 2.5%).
- Contribution timing — paying in at the start of the month rather than the end earns interest one period earlier. Using the example below, contributing at the start of each month instead of the end lifts the nominal result from $622,709 to $625,220 — a small but real difference.
- Retirement goal — turn on a target monthly income or a percentage of your current income, and the calculator adds the target capital, the gap, and the required monthly contribution to the result.
The result updates instantly, alongside a year-by-year chart and table so you can see how much of your final balance is money you paid in versus growth.
How the projection is calculated
The calculator combines two standard future-value formulas: one for the lump sum you already have, one for the stream of monthly contributions (a future value of an annuity):
Growth of your current savings: FV = P × (1 + i)^n
Growth of your contributions: FV = C × [((1 + i)^n − 1) / i]
where P is your current savings, C is your monthly contribution, i is the monthly return (annual return ÷ 12), and n is the number of months until retirement. Your projected capital is the sum of both.
Step-by-step example
Say you’re 35 now, plan to retire at 65 (a 30-year, 360-month horizon), have $20,000 saved, contribute $500 a month, expect a 6% annual return and 2.5% annual inflation, paying in at the end of each month.
- Monthly return: 6% ÷ 12 = 0.5% (i = 0.005).
- Your $20,000 grows on its own to roughly $120,452 over 360 months.
- Your $500-a-month contributions grow to roughly $502,257 over the same period.
- Add them together: projected capital at 65 = $622,709 (nominal — actual dollars in the year you turn 65).
- Over 30 years, 2.5% inflation multiplies prices by about 2.10×. Dividing $622,709 by that factor gives $296,872 in today’s purchasing power.
Both numbers are correct — they just answer different questions. The nominal figure is what your account statement will show; the real figure tells you what that amount will actually buy, in terms you can compare with prices today.
Nominal vs today’s money: why inflation matters
Inflation quietly shrinks the purchasing power of money you’re not spending yet. The calculator applies the classic relationship between nominal and real returns (the Fisher equation) to show both figures side by side, so a big-looking number in 30 years doesn’t lull you into a false sense of security.
The gap between nominal and real widens the longer your horizon and the higher inflation runs. Take someone 40 planning to retire at 60, with $10,000 saved and $300 a month going in, expecting only a 2% annual return against 5% inflation. Their real (inflation-adjusted) return is negative — about −2.86% a year — because prices are rising faster than their money is growing. The calculator still projects a real capital of about $38,952, but it flags the negative real return: at that return/inflation combination, your purchasing power is shrinking even while the nominal balance goes up.
Setting a retirement goal: two methods, one gap
If you turn on a retirement goal, the calculator shows you the capital you’d need using two different methods — deliberately, because they answer the question differently and neither is “more right”:
- The 4%/SWR method: divide your desired annual income by your safe withdrawal rate (commonly 4%). It’s a fixed percentage, historically chosen to survive bad 30-year market sequences without running the portfolio down to zero, regardless of the exact return path.
- The fixed-horizon annuity method: work out the capital that, drawn down evenly over a specific number of years at a specific real return, reaches exactly zero at the end. It uses your own assumptions about return and how long the money needs to last.
Continuing the example above (35 → 65, $20,000 saved, $500/month, 6% return, 2.5% inflation), say you’d like $4,000 a month in retirement (in today’s money), you’re comfortable with a 4% withdrawal rate, expect your money to last 30 years after retiring, and expect a 3% real return during retirement. The calculator returns:
- 4%/SWR target: $4,000 × 12 ÷ 4% = $1,200,000.
- Fixed-horizon annuity target: $940,821 — lower, because it assumes your capital keeps earning a real 3% while you draw it down over exactly 30 years, rather than aiming to never run out.
- Your projected capital in today’s money is $296,872 (from the growth example above) — so against the 4%/SWR target, you’re short by $903,128.
- To close that gap by retirement, you’d need to contribute a total of $2,386 a month — not $500 plus $2,386, but $2,386 total, replacing your current contribution.
If you expect any other income in retirement — a state pension, rental income, a spouse’s pension — you can enter it separately; it reduces the income you need to fund from your own savings before the target is calculated, but it’s never assumed automatically.
The 4% rule, the Trinity Study and FIRE
The “4% rule” traces back to financial planner William Bengen’s 1994 research and the 1998 Trinity Study, which tested how various withdrawal rates would have survived historical 30-year market cycles. More recent analysis, including Morningstar’s ongoing research, has suggested a safe withdrawal rate closer to a range of roughly 3.7%–4.7%, depending on the portfolio mix and time horizon — which is why the safe withdrawal rate field is one you can adjust rather than a fixed constant.
The same 25× shorthand (the inverse of 4%) underlies the FIRE (Financial Independence, Retire Early) movement: your “FIRE number” is simply your desired annual spending times 25. Set a younger retirement age and a higher desired income relative to your savings rate, and this calculator effectively becomes a FIRE calculator — the mechanics are identical, only the target retirement age changes.