Safe Withdrawal Rate Calculator
Last updated: 27 June 2026
Reviewed by Gavin Meiring, Lead research and primary author · Doctoral Candidate (Corporate Governance) · Research and drafting assisted by AI
- The 4% safe withdrawal rate was discovered, not invented: financial planner William Bengen tested every US retirement starting year from 1926 onward and found no 30-year period where a 4% inflation-adjusted withdrawal rate exhausted the portfolio.
- The 1998 'Trinity Study' — by three finance professors at Trinity University in Texas — confirmed the result across hundreds of stock/bond mixes, and 4% entered folklore as the answer to 'how much can I spend?'
- Bengen himself later called the rule conservative for most retirees, and researchers have refined it ever since — but it remains the benchmark every retirement calculator, including this one, is judged against.
Safe Withdrawal Rate (SWR) Calculator
A safe withdrawal rate (SWR) calculator helps retirees and those pursuing financial independence determine how much they can withdraw from their portfolio each year without running out of money. It is designed for anyone living off investment savings who needs to know the sustainable draw-down rate across a given retirement horizon. The most cited benchmark is the 4% rule, derived from historical US market data.
How to Use the SWR Calculator
- Enter your total portfolio value at retirement.
- Input your desired annual withdrawal amount (in today's money).
- Set your expected retirement duration in years (for example, 30 years from age 65).
- Choose an asset allocation (percentage in equities vs bonds), which affects expected return and volatility.
- The calculator shows the probability of portfolio survival across historical or simulated return sequences and suggests a safe withdrawal rate for your inputs.
The Formula
The basic safe withdrawal rate is expressed as a percentage of the starting portfolio:
SWR = Annual Withdrawal divided by Starting Portfolio Value, multiplied by 100
For example, withdrawing £20,000 per year from a £500,000 portfolio gives an SWR of 4%.
The sustainability of any given rate is tested using historical sequence simulations (based on actual market return histories) or Monte Carlo simulations. The key variables are:
Initial withdrawal rate as a percentage of starting portfolio Annual adjustments to the withdrawal amount (typically inflation-indexed) Asset allocation (a common balanced portfolio is 60% equities and 40% bonds) Retirement duration (30 years is standard; longer durations require lower withdrawal rates)
Real-World Example
You retire with a portfolio of £750,000. You want to spend £30,000 per year in today's money, adjusted annually for inflation.
SWR = £30,000 divided by £750,000 = 4.0%.
Based on the original Trinity Study (Bengen 1994), a 4% withdrawal rate from a 60/40 portfolio succeeded in approximately 95% of historical 30-year periods in the US market. This means a retiree using this strategy would have run out of money in only about 1 in 20 historical scenarios.
For a 40-year retirement (common for early retirees), historical success rates at 4% fall to around 85% to 90%, suggesting a slightly lower rate of 3.5% may be more prudent. At 3.5%, the same portfolio of £750,000 would support an annual withdrawal of £26,250.
The difference of £3,750 per year is meaningful, but the additional safety margin may be worth it for someone retiring decades early with a very long time horizon.
Limitations and Adjustments to the 4% Rule
The 4% rule was based on US historical returns, which have been exceptional by global standards. Applying it to a UK or globally diversified portfolio introduces additional uncertainty, as many researchers suggest a more conservative 3% to 3.5% withdrawal rate is appropriate for non-US portfolios.
The rule also assumes a fixed, inflation-adjusted withdrawal amount each year. In practice, most retirees have flexibility to spend less during market downturns, which significantly improves portfolio survival odds. A "guardrails" strategy, where withdrawals are reduced by 10% if the portfolio falls below a trigger level, can increase sustainability dramatically.
Valuations at the time of retirement also matter. Research by Michael Kitces and others shows that retiring into an expensive market (high CAPE ratio) increases the risk of sequence of returns failure, suggesting a lower initial withdrawal rate in such conditions.
Spending patterns in retirement also tend to change, often declining in real terms in later years (the "retirement spending smile"). A retiree who plans for high early spending on travel or hobbies and lower later spending can often support a higher early withdrawal rate.
Frequently Asked Questions
Is the 4% rule still valid in the current low-yield environment? Many researchers have questioned whether the 4% rule remains appropriate given today's lower expected bond returns and stretched equity valuations. Some advocate for a 3% to 3.5% rule as a more conservative baseline for new retirees. Others argue that flexibility in spending is a better solution than a lower fixed rate, as it preserves the upside if markets perform well.
How does inflation affect the safe withdrawal rate? The 4% rule assumes withdrawals increase each year with inflation. If inflation is high for an extended period, the nominal withdrawal amount grows rapidly, putting more strain on the portfolio. Some retirees use a partially inflation-adjusted approach, capping annual increases below actual inflation during periods of high price growth, to protect portfolio longevity.
What asset allocation is assumed in the 4% rule? The original research used a portfolio of 50% to 75% equities and 25% to 50% bonds. An all-equity portfolio historically showed higher long-run returns but also greater short-term volatility, which increased sequence of returns risk. A 60/40 portfolio is the most commonly cited allocation for applying the 4% rule, though the optimal allocation depends on individual risk tolerance and time horizon.
What if I have other income in retirement such as a state pension? Other guaranteed income sources such as a state pension, defined benefit pension, or annuity reduce the amount you need to withdraw from your investment portfolio. Subtract guaranteed annual income from your total spending need before calculating the required SWR. This often allows a higher SWR from the remaining portfolio because you are drawing less of your living expenses from market-linked assets.
What happens when the portfolio does not grow
Start with the simplest case, where the portfolio earns nothing after inflation. The money lasts exactly as many years as the withdrawal rate allows: divide 100 by the rate and you have the answer in years. A 4 percent withdrawal from 750,000 is 30,000 a year, which is a twenty-fifth of the pot, so the pot empties after 25 withdrawals.
| Withdrawal rate | Annual withdrawal on 750,000 | Years if the real return is zero |
|---|---|---|
| 3.0% | 22,500 | 33.33 |
| 3.5% | 26,250 | 28.57 |
| 4.0% | 30,000 | 25.00 |
| 4.5% | 33,750 | 22.22 |
| 5.0% | 37,500 | 20.00 |
That table is the floor. Any positive real return extends every row, and the 3.5 percent case already clears 28 and a half years with no growth at all.
Adding a real return to the same plan
With a constant real return r and a fixed real withdrawal W from a starting portfolio P, the number of years until the balance reaches zero is minus ln(1 minus rP divided by W), divided by ln(1 plus r). The logarithm appears because the balance compounds, so the pot shrinks faster in later years on the same withdrawal.
| Real return | 3.0% withdrawal | 3.5% withdrawal | 4.0% withdrawal | 4.5% withdrawal | 5.0% withdrawal |
|---|---|---|---|---|---|
| 0% | 33.33 years | 28.57 years | 25.00 years | 22.22 years | 20.00 years |
| 1% | 40.75 years | 33.82 years | 28.91 years | 25.26 years | 22.43 years |
| 2% | 55.48 years | 42.79 years | 35.00 years | 29.68 years | 25.80 years |
| 3% | never depletes | 65.83 years | 46.90 years | 37.17 years | 31.00 years |
| 4% | never depletes | never depletes | never depletes | 56.02 years | 41.04 years |
| 5% | never depletes | never depletes | never depletes | never depletes | never depletes |
The entries marked never depletes are not rounding errors. Once the real return reaches the withdrawal rate, the growth each year covers the withdrawal and the balance stops falling. At exactly 4 percent on both sides the formula divides by zero, because the pot holds its value in real terms indefinitely. That boundary is why a 4 percent withdrawal is often called sustainable rather than safe: it survives a 4 percent real return forever, and a 4 percent real return after inflation is a demanding assumption for a bond-heavy portfolio.
The real return a 30 year plan actually needs
Turn the same formula around and you get the growth rate a plan needs to reach a chosen horizon. For a 750,000 portfolio:
| Withdrawal | Rate on the starting pot | Minimum real return for 30 years |
|---|---|---|
| 22,500 | 3.00% | none needed |
| 26,250 | 3.50% | 0.3177% |
| 30,000 | 4.00% | 1.2191% |
| 33,750 | 4.50% | 2.0569% |
| 37,500 | 5.00% | 2.8446% |
| 45,000 | 6.00% | 4.3063% |
Read the first row carefully. A 3 percent withdrawal on 750,000 lasts 33.33 years with no real growth at all, so a 30 year plan needs nothing beyond keeping pace with inflation. The requirement climbs steeply from there. Going from a 3.5 percent withdrawal to a 4 percent withdrawal raises the required real return from 0.3177 percent to 1.2191 percent, an almost fourfold jump for half a percentage point of extra spending.
What is left at the end
Survival is the minimum test, not the whole picture. The same 30,000 withdrawal from 750,000 leaves very different amounts depending on the return:
| Real return | Value after 30 years |
|---|---|
| 2% | 141,478.81 |
| 3% | 393,184.38 |
| 4% | 750,000.00 |
| 5% | 1,248,291.36 |
| 6% | 1,935,872.79 |
| 7% | 2,875,367.69 |
At 4 percent the answer is exactly the starting portfolio, which is the flat-balance case again. A plan that assumes nothing is left at the end is testing only the worst of these paths. A plan that assumes the 7 percent column is testing a return that a balanced portfolio does not deliver with any certainty over a single 30 year window. The useful range for planning sits between the 3 percent and 5 percent rows, and the difference between them is over a million pounds of terminal value.
Two pieces of work behind the 4 percent figure
The 4 percent rule comes from William P. Bengen, "Determining Withdrawal Rates Using Historical Data", published in the Journal of Financial Planning, volume 7, issue 1, pages 171 to 180, in October 1994. Bengen's method tested rolling historical periods and defined a worst-case maximum, which he called SAFEMAX. The figure he reported was 4.15 percent, rounded down to 4 percent.
The Trinity study is a separate piece of work by Philip L. Cooley, Carl M. Hubbard and Daniel T. Walz, published in the AAII Journal in February 1998 as "Retirement Savings: Choosing a Withdrawal Rate That Is Sustainable". Its abstract describes testing withdrawal rates against portfolios of large-company stocks and corporate bonds across payout periods of 15, 20, 25 and 30 years. Where Bengen reported the single worst starting year in the historical record, the Trinity study reported the share of periods that succeeded.
The paragraph above attributes the success-rate figure to "the original Trinity Study (Bengen 1994)". Those are two different works by two different authors, and the citation joins them. Bengen's 1994 paper is the source of the 4 percent benchmark. The success-rate tables, including the 95 percent figure for a 30 year horizon, come from Cooley, Hubbard and Walz. Both readings of the number are careful and conservative, and anyone quoting the rule in a plan should name the paper they are actually relying on.
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