You want a clear answer: how long will your retirement savings last? Good. That means you want control. I’ll give you a simple calculator method, the exact formula you can use on a spreadsheet, and a real anonymous case study for 400k. No fluff. Just the numbers and the human-side rules you can actually use. 😊
What this calculator answers (and what it doesn’t)
This calculator estimates how many years your portfolio will last given a starting balance, an annual withdrawal (either a percentage or an amount), an expected real return, and whether withdrawals are inflation-adjusted. It uses a deterministic model: the portfolio grows at a steady real rate and you withdraw a fixed real amount each year. That gives clean, repeatable answers you can reason with.
What it doesn’t do: it does not run Monte Carlo scenarios, predict market crashes, or replace a full financial plan. But it answers the core question you came here to ask: if I have X saved and I take Y each year, how many years until the money runs out (or doesn’t)?
The simple math behind the calculator
We model the balance this way: each year the portfolio grows by a real return r, then you remove a real, inflation-adjusted withdrawal W. So the balance B each year follows B\_next = B \* (1 + r) − W.
If withdrawals are constant in real terms (you increase them by inflation each year), there’s a closed-form formula for how many years N until the balance hits zero:
N = log( W / (W − B0 \* r ) ) / log(1 + r)
Important boundary: if W ≤ B0 \* r, the formula breaks because your withdrawal is no larger than the portfolio’s yearly real earnings. In that case the portfolio can support the withdrawal indefinitely (ignoring taxes, sequence risk, and fees).
How to use the formula step by step
- Decide whether your withdrawal is a percent of the starting balance or a fixed real amount. Example: 4% of 400k = 16,000 per year.
- Choose an expected real return r (expected nominal return minus inflation). Common conservative choices: 1%, 2%, 3% real.
- Plug values into the formula. If the denominator inside the log is zero or negative, your withdrawal is sustainable in real terms.
Case study — How long will 400k last in retirement?
Let’s test three typical withdrawal choices and three conservative real-return scenarios. This is anonymous but real: think of someone who has saved 400,000 and is trying to decide a safe withdrawal.
| Withdrawal | Amount (real) | Years at 1% real | Years at 2% real | Years at 3% real |
|---|---|---|---|---|
| 4% rule | 16,000 | 29 years | 35 years | 47 years |
| 3% rule | 12,000 | 41 years | 56 years | Indefinite (sustainable) |
| Fixed real spending | 25,000 | 18 years | 20 years | 22 years |
Quick takeaways from the table:
If you withdraw 4% in real terms from 400k (16k/year), expect the money to last roughly three decades under conservative real-return assumptions. Drop the withdrawal to 3% and your runway grows a lot — often long enough to cover typical retirements.
Why the same numbers can give very different real-life outcomes
Because the deterministic model assumes smooth returns. Real life does not. A few things to keep in mind:
- Sequence of returns risk: early big losses while you’re withdrawing speed up depletion. Two retirees with the same average return can have very different outcomes.
- Inflation matters: the formula above uses real returns. If you use nominal returns in the math but the withdrawal is inflation-adjusted, you’ll misestimate longevity.
- Fees and taxes chew away returns. Always include them in your expected real return.
Practical ways to make 400k last longer
If you’re staring at 400k and thinking it’s not enough, you have options. They trade off risk, effort, and lifestyle.
Lower your withdrawal rate. Cutting spending from 16k to 12k a year is dramatic. Small changes compound.
Delay full withdrawals by working part-time. Even a few years of earnings or lower withdrawals early on can protect you from early market downturns.
Adopt a bucket strategy. Hold 1–3 years of cash for living expenses, keep the rest invested for growth. This helps ride out volatility without forced selling.
Consider guaranteed income for longevity risk. An annuity or partial annuitization shifts risk away from you, although it costs money and reduces flexibility.
Reduce fees and taxes. Low-cost index funds and tax-aware withdrawal sequencing can add years to your portfolio.
How to build this calculator in a spreadsheet (simple template)
Step 1: Put starting balance B0 in a cell.
Step 2: Put real return r in another cell (as decimal).
Step 3: Put annual real withdrawal W in a third cell.
Step 4: In the next row calculate B1 = B0 \* (1 + r) − W. Copy down until balance ≤ 0. Count rows — that’s years of runway.
If you prefer the closed form for constant real withdrawals, use the formula given earlier to compute N directly. Useful when you need an instant answer.
Rules of thumb I use personally when advising readers
I keep things anonymous and practical. Here are the rules I usually suggest for readers before they get too attached to any exact year count:
Assume lower returns than you hope. Hope is not a plan.
Aim for a withdrawal rate that matches your comfort with risk. 3% is conservative; 4% is common but not guaranteed; anything above 4% is risky unless you accept lifestyle cuts or more work later.
Always stress-test with bad early returns and higher inflation scenarios.
Quick checklist before you commit to a retirement withdrawal plan
Do you have an emergency buffer of cash for 1–3 years of expenses? Have you included taxes and fees in your math? Do you understand how your pension or social benefits (if any) layer with your drawdown? If the answer to any is no, pause and adjust before making irreversible choices.
When the calculator is most useful
Use it when you need an evidence-based sanity check. It’s great for:
Estimating whether you can retire now.
Comparing how many more years you’ll be comfortable if you save another 50k.
Testing the value of small lifestyle changes (e.g., cutting withdrawal by 10%).
Common mistakes people make with retirement calculators
Relying on a single return estimate. Treat returns as a range, not a point.
Ignoring sequence of returns. Early market crashes while withdrawing are the biggest danger.
Forgetting taxes and fees. They aren’t small — they compound over decades.
Assuming perfect health and no surprise expenses. Longevity risk and medical costs matter.
Final honest advice
These calculators don’t remove uncertainty, but they reduce fear. Use the math to make decisions, not to predict the future. If 400k is your starting point, you can make it work — but strategy matters. Lower withdrawals, phased retirement, side income, and low costs are your best levers. You don’t need perfection. You need a plan you can live with and adjust.
Further reading and tools
Run the numbers, iterate, and test a few scenarios. If you want, run the closed-form formula for a few r values (1%, 2%, 3%) and see how sensitive your years of runway are to small changes. The difference between 1% and 2% real return can be decades of retirement life.
FAQ
How long will my retirement last with 400k?
It depends on your withdrawal amount and real return. As a rule of thumb, a 4% real withdrawal (16k/year) from 400k will likely last multiple decades under reasonable returns, but could deplete in about 29–47 years under conservative real-return scenarios. Lower withdrawals or higher real returns lengthen the runway significantly.
What is a safe withdrawal rate?
There’s no single answer. Many people use 4% as a starting rule, but 3% is much safer and can stretch your savings considerably. Your personal safe rate depends on your tolerance for risk, expected returns, and whether you’ll accept adjustments in bad years.
Should I use nominal or real returns in the calculator?
Use real returns when you plan to inflation-adjust your withdrawals. Real return = nominal return − inflation. That keeps the math consistent with inflation-indexed spending.
What if the formula gives infinite years?
That means your withdrawal is no larger than the portfolio’s yearly real earnings (W ≤ B0 \* r). In plain terms: your portfolio can sustain that withdrawal indefinitely in the deterministic model. Remember to factor in fees, taxes, and sequence risk.
How does sequence of returns risk affect the result?
Sequence of returns risk means that early-year negative returns while you’re withdrawing cause permanent harm that averages don’t show. Two portfolios with the same average return can behave very differently if one has big early losses. That’s why bucket strategies and short-term cash reserves help.
Does the calculator include taxes and fees?
Not automatically. You should reduce your expected real return by expected fees and the real after-tax impact of withdrawals to make the results realistic.
How do I account for Social Security or pensions?
Treat guaranteed income as a separate income stream. Subtract expected annual benefits from your withdrawal need and plug the remainder into the calculator. That reduces how much you must draw from your portfolio.
Can I use this calculator if I plan to earn part-time in retirement?
Yes. Any expected income that reduces your withdrawal requirement extends the runway. Model reduced withdrawals in early years to see the effect.
What if I want to withdraw a fixed nominal amount that is not inflation-adjusted?
If you withdraw a fixed nominal amount, the real purchasing power of your withdrawals will decline with inflation. The deterministic formula above assumes inflation-adjusted (real) withdrawals. For nominal fixed withdrawals, either model nominal returns and nominal withdrawals, or convert nominal withdrawals to real terms before using the formula.
Is the 4% rule still valid?
The 4% rule is a historical guideline built around safe withdrawal over roughly 30 years. It’s useful as a starting point but not a guarantee — shifts in market returns, inflation, and low-yield environments can change outcomes. Treat it like a test, not gospel.
How should I pick an expected real return?
Be conservative. Historically, stocks provide higher returns but more volatility, while bonds give lower but steadier returns. For long retirements, many planners use 1%–3% real as a conservative range to test against.
What if my expected lifespan is shorter than the calculated runway?
That’s a good problem to have. If your calculated runway exceeds your expected lifespan, you can increase spending, leave a legacy, or reduce investment risk. Still run stress tests in case you live longer than expected.
How do I include healthcare or unexpected large expenses?
Model those as lump-sum withdrawals in the years they occur, or increase your planned withdrawal to include a buffer. Another method is to keep a contingency bucket separate from the investable portfolio.
Can I adjust withdrawals dynamically?
Yes. Dynamic withdrawal strategies reduce withdrawals after bad market years and increase them after good years. They trade predictability for longevity.
Should I buy an annuity?
An annuity can cover longevity risk by converting a portion of your savings into guaranteed lifetime income. It reduces portfolio risk but costs money and reduces liquidity. Evaluate carefully and consider partial annuitization.
Will investing more aggressively make my money last longer?
Potentially, yes — higher expected returns lengthen runway. But greater equity exposure increases sequence-of-returns risk, especially early in retirement. Balance growth needs with short-term cash to avoid forced selling.
How do withdrawal taxes change the calculation?
If withdrawals are taxed, your effective net withdrawal is smaller. Either increase your gross withdrawal to cover taxes or lower expected real returns to reflect the after-tax return. Both approaches work; be explicit about assumptions.
What’s the difference between a percent-based withdrawal and a floor-based withdrawal?
Percent-based withdrawals (e.g., 4% of portfolio each year) automatically adjust with portfolio size, which reduces depletion risk after losses but lowers predictability. Floor-based withdrawals guarantee a minimum income (often covered by safe assets or guaranteed income) and let the rest fluctuate.
How frequently should I recalculate my retirement runway?
At least annually, and whenever there is a major life change: big market moves, large expenses, significant changes to health, or a new guaranteed income stream. Regular checks keep the plan honest and adaptable.
Does inflation make a big difference?
Yes. Higher inflation increases the real withdrawal needed and shortens runway if returns don’t keep up. That’s why using real returns for the math matters.
Can I use a Monte Carlo instead of this calculator?
Monte Carlo is useful for seeing a range of possible outcomes given random returns. The deterministic calculator gives clear intuition and closed-form results. Use both: Monte Carlo for probability, deterministic for clarity.
How do I handle large one-off windfalls or losses?
Treat windfalls as a balance increase and re-run the calculator. Treat large losses the same, but also consider pausing withdrawals or cutting spending to avoid compounding the problem early.
What is a safe sequence of withdrawals for the first five years of retirement?
Conservative planners often recommend holding multi-year cash reserves to cover the first 1–3 years of withdrawals, reducing the need to sell in a downturn. Another approach is to reduce withdrawals modestly in the first few years if markets fall.
How should I present assumptions to my partner or family?
Keep it simple: list starting balance, withdrawal amount, assumed real return range, and the resulting range of years. Discuss the what-ifs (health, market bad years, lifestyle changes) and agree on guardrails for adjustments.
What’s the single most impactful lever to extend runway?
Reducing the withdrawal rate. Small percent reductions compound into many more years of financial independence. Next best: adding guaranteed income or delaying full withdrawals by working part-time.