Drawdown & Safe Withdrawal Simulator — United States
Accumulation calculators tell you when you can stop. This one tells you whether stopping was a good idea. It runs thousands of randomised market paths against your portfolio and spending plan, then reports how often the money lasted — and what the range of outcomes actually looks like.
The retirement you are testing
Everything here is in today's dollars.
That is a 4.00% starting withdrawal rate.
A 40-year retirement.
How you spend
Spend the same real amount every year regardless of markets. The classic Trinity study assumption, and the harshest test.
Adds an indexed benefit from age 67.
Asset mix
Cash is whatever is left: 5%.
Success rate over 40 years
68.8%
Across 4,000 simulated market paths, that is how often the portfolio still had money at age 95. When it failed, the median run ran dry around age 83.
- Starting withdrawal rate
- 4.00%
- Safe spend at 95%
- $29,591
- Implied safe rate
- 2.37%
General information, not advice
Range of outcomes
Every simulated market path, summarised. The dark band holds the middle half of outcomes; the pale band holds 80%.
- Median path
- 25th–75th
- 10th–90th
Where you end up
The spread of final balances across every simulation. The leftmost bar is the share of runs that ran out of money; the last bar collects the top 5%.
- Median ending balance
- $1,175,180
- Poor outcome (10th)
- $0
- Good outcome (90th)
- $9,062,971
In today's dollars
Assumptions and limitations
Every result above rests on these assumptions, and each can be changed in the inputs. Why the defaults are reasonable
- Shares
- 6.5% real, 17.5% volatility
- Bonds
- 2.0% real, 7.0% volatility
- Cash
- 0.5% real, 1.2% volatility
- Share–bond correlation
- 0.10
- Fees
- 0.20% a year
- Simulations
- 4,000
Limitations
- Returns follow a normal distribution. Real markets have more extreme years than a normal distribution allows, so the success rate may overstate how safe a plan is.
- No tax. Withdrawals and investment earnings are not taxed. Spending should already allow for the tax you expect to pay, or the success rate will be too high.
- The defaults reflect long-run history. If future returns are lower than in the past, success rates will be lower too. Try the market assumptions a notch lower.
- Social Security is a flat amount you add. Your actual benefit depends on your earnings record and the age you claim.
Reading this honestly
What the number does and does not tell you.
A success rate is not a probability of a good life — it is the share of simulated paths where a rigid spending plan never hit zero. Real retirees notice a bad decade and adjust. That is exactly why the guardrails rule scores so much better than the fixed rule on identical assumptions: modest flexibility is worth more than a larger portfolio.
These paths are drawn from a normal distribution around the return and volatility you set. That is a reasonable model, but real markets have fatter tails and returns are not independent from one year to the next, so a difference of a few points — 94% against 97%, say — is within the model’s margin of error.
Social Security acts as an inflation-linked floor under your spending. Turning it on is usually the single largest change to the success rate, and for most households it is the more realistic assumption.
How this works
What are the odds my money outlasts me?
Sequence of returns is the real risk
Two retirements with identical average returns can end very differently depending on when the bad years arrive. A crash in your first five years forces you to sell more units to fund the same spending, and the portfolio may never recover. That is why an average return is not enough and a distribution of paths is.
Everything is in real terms
Returns, spending and final balances are all inflation-adjusted, so a dollar in year one means the same as a dollar in year forty. This makes the success rate directly comparable to the Trinity study and other published safe-withdrawal research.
Flexibility beats size
Switch the spending rule from fixed to guardrails and watch the success rate move. Being willing to trim spending by ten percent in a bad stretch is usually worth more than several years of extra saving — and it is a far cheaper form of insurance.
What the model assumes
Annual returns are drawn from a normal distribution around the mean and volatility you set, with a correlation between shares and bonds. Real markets have fatter tails and some mean reversion, so treat the exact percentage as an indicator rather than a forecast.
Where the 4% rule comes from
In 1994 William Bengen looked at every 30-year retirement in US history since 1926 and found that an initial withdrawal of about 4%, then raised with inflation, survived all of them with a balanced portfolio. The 1998 Trinity study by Cooley, Hubbard and Walz reached a similar answer with success rates across many mixes and horizons. In his 2025 book, Bengen put the figure for a 30-year retirement nearer 4.7%, using a broader mix of assets.
This simulator tests your own withdrawal rate instead of borrowing theirs. It draws a year of returns for shares, bonds and cash thousands of times over, applies your spending rule and reports how often the money lasted to the end age you set.
Longer retirements need more margin
Both studies looked at 30 years. Someone retiring at 45 is planning for 45 or 50, and a rate that survived every 30-year period in history does not survive every 50-year one. Set the end age to match your plan and the success rate shows the difference directly.
Sequence risk: why the order of returns matters
Two retirements with the same average return can end very differently. A fall in the first few years forces you to sell more to fund the same spending, and those shares are not there for the recovery. A simulation that varies the order of returns tells you more than a single average.
The "Poor outcome (10th)" figure shows what the worst tenth of paths left behind. If it is uncomfortable, the levers are spending, the spending rule, the asset mix and the end age.
Spending rules
- Fixed spends the same real amount every year regardless of markets: the Trinity study's assumption and the harshest test.
- Guardrails trims spending when the withdrawal rate drifts too far above where it started and raises it when the portfolio runs ahead. A modest willingness to cut in bad years usually improves the success rate a lot.
- % of portfolio takes the same percentage of whatever the balance is each year, with a floor under spending. The portfolio never fully runs dry, but your income rises and falls with markets.
Social Security and required distributions
Switch on "Include Social Security" to add $24,000 a year from 67, kept level in today's dollars. Benefits can start from 62 at a reduced rate or be delayed to 70 for a larger one (SSA, SSA); enter your own estimate for a more meaningful success rate.
Required minimum distributions from traditional 401(k)s and IRAs start at 73, or 75 for anyone born in 1960 or later. They force money out of the account, not into spending, so the simulator does not apply them.
Frequently asked questions
What is a safe withdrawal rate?
There is no single safe rate. 4% held through every 30-year US retirement in Bengen's data; longer horizons point lower, and willingness to cut spending in bad years points higher. The simulator shows how often your rate lasts on your assumptions, and the highest spending that meets your target success rate.
What does the success rate mean?
The share of simulated market paths in which the portfolio paid your spending every year to the end age. A 90% success rate means one path in ten ran out early. The safe spend is the highest spending that meets your target success rate, 95% by default.
Does the simulator use historical returns?
No. It draws returns from a normal distribution around the real return and volatility you set, with a correlation between shares and bonds. Real markets have more extreme years, so treat the success rate as an indicator rather than a forecast.
Are the returns real or nominal?
Real. Returns, spending and balances are all in today's dollars, so results compare directly with the Trinity study and other published research.
Does the simulator include taxes?
No. Set your spending to include the federal and state tax you expect to pay on withdrawals; the FIRE calculator models tax in more detail.
Sources
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