Trinity Study Portfolio Success Calculator
Historical 30-year portfolio success rate for any withdrawal rate + stock/bond allocation, from the canonical Trinity Study (Cooley/Hubbard/Walz 1998). Free.
Trinity Study Portfolio Success Calculator
The Trinity Study asked a precise question: across every historical 30-year retirement since 1926, how often did an inflation-adjusted withdrawal survive the full period? Enter a withdrawal rate and a stock/bond allocation to see the historical success rate — and how much the allocation changes the odds.
Success rate by allocation (at 4.0%)
How to Use the Trinity Study Calculator
Pick your withdrawal rate
The percentage of your starting portfolio you'd withdraw in year one, then increase by inflation each year after. 4% is the classic Trinity/Bengen figure; FIRE retirees with 40+ year horizons often use 3.25–3.5%.
Set your stock allocation
The share of the portfolio in stocks (the rest in bonds). This is the variable the Trinity Study made famous: too few stocks and inflation erodes the portfolio; too many and volatility threatens it. The historical sweet spot sits around 50–75% stocks.
Read the headline success rate
The share of historical 30-year periods in which that rate + allocation never ran the portfolio dry. 95%+ is robust; below 90% means you're relying on an above-average sequence of returns.
Compare across allocations
The grid shows the same withdrawal rate at all five allocations. Use it to see how much moving from, say, 25% to 75% stocks improves your odds — usually far more than people expect at higher withdrawal rates.
The Trinity Study — Where the 4% Rule Got Its Confidence Interval
What the Three Professors Actually Did
In 1998, three finance professors at Trinity University in San Antonio — Philip Cooley, Carl Hubbard, and Daniel Walz — published "Retirement Savings: Choosing a Withdrawal Rate That Is Sustainable" in the AAII Journal. William Bengen's 1994 paper had already proposed the 4% rule, but the Trinity Study reframed the question in the language retirees actually care about: not "what is the single safe rate?" but "for a given withdrawal rate and stock/bond mix, what percentage of historical periods succeeded?" They backtested every overlapping retirement window from 1926 onward using US large-cap stock returns and high-grade corporate bond returns, across five allocations (100/0, 75/25, 50/50, 25/75, 0/100) and a range of withdrawal rates, for horizons of 15, 20, 25, and 30 years. The output was a now-famous grid of success percentages.
The headline finding: an inflation-adjusted 4% withdrawal from a portfolio with at least 50% stocks succeeded in roughly 95% of historical 30-year periods. Push the rate to 5% and success collapses — to about 67% at 50/50 and 82% at 75/25. Drop to 3% and essentially every historical period survived at any equity-heavy allocation. The study made two things undeniable: withdrawal rate dominates the outcome, and a meaningful stock allocation is not optional — a 100% bond portfolio failed more than half the time even at 4%, because fixed-income returns couldn't outrun inflation over 30 years.
"The Trinity Study's quiet revolution was the word 'probability'. It turned 'how much can I spend?' from a single risky number into a distribution — and showed that the bond-heavy 'safe' portfolio was often the riskiest of all over a 30-year retirement."
How to Read a Success Rate — and Its Limits
A 95% historical success rate does not mean a 95% chance your retirement will work; it means that in the 1926–present US data, 95% of 30-year windows survived. That sample is dominated by the 20th-century US equity market, which Wade Pfau's international research later showed was an outlier on the favorable side. It also excludes the future: today's high equity valuations and the low-yield bond environment of the last decade are reasons modern researchers (Pfau, Kitces, Karsten "Big ERN" Jeske) lean toward 3.25–3.5% for long horizons. The Trinity tables are also strictly 30-year — a 45-year-old retiring early faces a 50-year horizon the study never tested, where safe rates fall further. Treat the success rate as a well-anchored historical baseline, not a guarantee, and pair it with a cash buffer and willingness to trim spending after a bad year.
For retirees in Singapore, Malaysia, and the wider ASEAN region, the Trinity framework still travels, but the inputs need translating. CPF (Singapore) and EPF (Malaysia) already provide a partly annuitised, lower-volatility income floor — so the portfolio the 4%/Trinity math applies to is only the supplementary investment pot on top of those schemes, which sharply reduces the required portfolio. A globally diversified portfolio anchored in US and developed-market equities can reasonably borrow the 3.5–4% range; a portfolio concentrated in a single smaller home market historically supported a lower safe rate. Currency matters too: if you earn in SGD or MYR but hold USD assets, exchange-rate swings add a layer of sequence risk the original US-only study never modelled. The sensible adaptation is to lean toward the conservative end of the grid and let CPF/EPF carry the non-negotiable spending.
10 Facts About the Trinity Study
The Trinity Study (1998) was authored by Cooley, Hubbard & Walz of Trinity University, Texas — hence the name.
It reframed Bengen's 4% rule as a grid of success probabilities across withdrawal rates and stock/bond mixes.
An inflation-adjusted 4% withdrawal survived ~95% of historical 30-year periods at 50%+ stocks.
At 5%, success fell to ~67% (50/50) and ~82% (75/25) — small rate change, large odds change.
A 100% bond portfolio failed more than half the time at 4% — inflation outran fixed income over 30 years.
The study used US data from 1926, large-cap stocks + high-grade corporate bonds, overlapping windows.
The historical sweet spot was 50–75% stocks — enough growth to beat inflation, enough bonds to dampen crashes.
Original horizons were 15, 20, 25 and 30 years; this tool uses the canonical 30-year table.
Wade Pfau's international study found the US was an outlier — many countries had lower safe rates.
For 40+ year (FIRE) horizons, modern researchers favour 3.25–3.5%, below the classic 4%.
Frequently Asked Questions
- A 1998 paper by three Trinity University professors (Cooley, Hubbard, Walz) that tested retirement withdrawal rates against historical US market data from 1926. For each combination of withdrawal rate and stock/bond allocation, it reported the percentage of historical 30-year periods in which an inflation-adjusted withdrawal never exhausted the portfolio. It's the study that gave the 4% rule its famous "~95% success" confidence figure.
- Bengen's 4% rule (1994) answered "what is the maximum safe rate?" with a single number. The Trinity Study answered "for a given rate AND allocation, what fraction of history succeeded?" — turning one number into a probability grid. Our companion safe-withdrawal-rate-calculator applies the 4% rule to turn a portfolio into a spend; this tool shows the historical odds behind a chosen rate and allocation.
- No. It means 95% of historical 30-year windows in the 1926–present US data survived. The future may differ — today's high stock valuations and the low-yield bond era are reasons many researchers now use 3.25–3.5% for long horizons. The US sample was also unusually favourable versus other countries. Read the success rate as a strong historical baseline, not a forward-looking guarantee.
- Over a 30-year retirement, inflation is the silent killer. A bond-heavy portfolio feels "safe" because it doesn't swing much, but its returns historically couldn't outrun decades of inflation while you withdrew from it — a 100% bond portfolio failed more than half the time at 4%. Stocks provide the growth that keeps the portfolio ahead of inflation. The Trinity grid shows the historical sweet spot was 50–75% stocks: enough growth, with bonds to soften crashes.
- The canonical 30-year table — the horizon the Trinity Study is best known for and the standard for a traditional retirement starting in your 60s. Shorter horizons (15–25 years) had higher success rates; longer horizons (40–50 years, common for early retirees) had lower ones. If you're retiring early, treat the 30-year figures as optimistic and lean toward a lower withdrawal rate, or use our safe-withdrawal-rate-calculator which discusses 3.0–3.5% for 40+ year horizons.
- No — the success rate applies only to portfolio withdrawals. Guaranteed income streams (US Social Security, a pension, Singapore CPF LIFE, Malaysia EPF) are separate and reduce the spending your portfolio must cover. The right approach: subtract those income streams from your target spending, then apply the withdrawal rate only to the remaining gap. This often shrinks the required portfolio dramatically.
- Yes. The figures here are for the inflation-adjusted method: withdraw the chosen percentage of the starting portfolio in year one, then increase that dollar amount by inflation every subsequent year, regardless of market performance. The Trinity Study also reported a "non-inflation-adjusted" set with higher success rates, but the inflation-adjusted version is the realistic one — your spending needs rise with prices.
- Four levers: (1) lower the withdrawal rate — even 0.5% makes a large difference; (2) move toward the 50–75% stock sweet spot if you're too bond-heavy; (3) build a 2–3 year cash buffer so you don't sell stocks during a crash (mitigates sequence-of-returns risk); (4) plan to trim spending 10% after a bad market year (the Guyton-Klinger guardrails). Part-time income in the first decade of retirement is also one of the most powerful fixes.
- The framework travels; the numbers don't transfer directly. The study used 20th-century US returns, which were exceptionally strong. Wade Pfau's research across 20 countries found many had lower safe rates. For ASEAN investors, a globally diversified portfolio anchored in developed-market equities can borrow the 3.5–4% range, but a portfolio concentrated in one smaller home market historically supported less. Add currency risk if you spend in SGD/MYR but invest in USD assets, and let CPF/EPF cover your essential spending.
- No. The Trinity Study uses historical "sequence" backtesting — it replays actual overlapping 30-year windows of real returns. Monte Carlo instead generates thousands of random return paths from an assumed distribution. Both have merits: historical backtesting captures real correlations and crashes that occurred together; Monte Carlo explores paths history hasn't produced yet. Many planners look at both. This calculator reports the historical (Trinity) result.
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