What is the 4 percent rule?
The 4% rule is the closest thing personal finance has to a load-bearing wall. It states that if you withdraw 4% of a balanced portfolio in your first year of retirement and increase the dollar amount with inflation every year after, the money will survive at least 30 years in nearly every historical market. Financial independence math is built on top of it: if 4% is safe, then the portfolio you need is simply 25× your annual spending — the famous “multiply by 25” that turns an abstract dream into a number.
The rule came from Bill Bengen's 1994 research and the 1998 Trinity Study, which replayed US stock-and-bond portfolios across every 30-year retirement window since 1926. Withdrawal rates of 4% survived virtually all of them. Not all — and that nuance is where honest planning starts.
The formula, and why the rate is a lever
The whole system is one division:
FIRE number = annual spending ÷ safe withdrawal rate (SWR)
At the classic 4%, that's spending × 25. The reason this calculator promotes the SWR slider to a core input is that 4% is a starting point, not scripture. Each rate implies a different multiplier and a different life:
- 3.25% — very-early-retirement grade: spending × ~31
- 3.5% — the modern conservative favorite: spending × ~29
- 4.0% — the classic Trinity figure: spending × 25
- 4.5% — aggressive, shorter horizons or pension backstops: spending × ~22
Two adjustments run under the hood. Inflation is handled with real returns — converted exactly as (1 + nominal) ÷ (1 + inflation) − 1, because naive subtraction overstates a typical 30-year portfolio by about 3–4% at these assumptions. And if your nest egg sits in pre-tax accounts, the optional tax field grosses up the target so the 4% covers what the IRS takes, not just what you spend. A 7% nominal return against 3% inflation is a 3.88% real return — small difference per year, big difference per decade.
A worked example
Riley spends $4,000 a month — $48,000 a year — and has $150,000 invested, adding $800 a month.
- At the classic 4%: FIRE number = $48,000 × 25 = $1,200,000. Riley is 12.5% of the way there.
- Slide to 3.5% for a 50-year horizon: target becomes ~$1.37M. The same savings rate needs roughly two more years of compounding.
- Slide to 4.5% because a small pension covers the floor: target drops to ~$1.07M, pulling the finish earlier instead. That sensitivity — 3.25% to 4.5% spans years of your life — is exactly what the slider makes visible.
Where the rule breaks (and what to do instead)
The 4% figure assumes a 30-year horizon, US-only history, and a rigid withdrawal pattern. Retiring at 35 means a 50-year horizon — historical success rates at 4% sag for those, so conservative planners use 3.25–3.5%. It assumes steady spending, while real retirees spend more in go-go years and less later. And it was never a spending guarantee: it's a historical frequency, not physics. The robust modern approach is flexible — guardrails that cut withdrawals ~10% after bad market years, a cash buffer for the first recession, and a withdrawal rate chosen for your horizon, not a headline. Use this calculator to see the price of each choice, then treat the verdict as a plan to revisit, not a certificate.
Frequently asked questions
What is the 4 percent rule?
The 4% rule says you can withdraw 4% of your portfolio in year one of retirement, raise it with inflation each year, and the money will very likely last 30+ years. It comes from the Trinity Study and Bill Bengen's historical simulations of US stock-and-bond portfolios across every retirement start date since 1926.
Is the 4% rule still valid today?
As a planning heuristic, yes; as a guarantee, no. It's based on US historical returns, which were kinder than most countries experienced, and 30-year horizons don't fit early retirees who may need 50+ years. Modern research (Bengen himself, and Big ERN's Safe Withdrawal Series) suggests 3.25–3.5% for very long horizons. Use the slider: the difference between 4% and 3.5% is a 14% larger portfolio.
How do I calculate my FIRE number with the 4% rule?
Multiply your annual spending by 25 (that's 100 ÷ 4). Spending $48,000 a year means a $1.2 million portfolio. This calculator does the division for you at any withdrawal rate you choose — 3.25% means multiplying by about 31, while a bolder 4.5% means about 22.
Does the 4% rule account for taxes and inflation?
Inflation, yes — withdrawals rise with CPI in the classic formulation. Taxes, only indirectly: the 4% is gross withdrawals, so if your portfolio is in traditional (pre-tax) accounts, set the tax-rate field and the calculator grosses up your spending target to cover what the IRS will take first.
What happens if I withdraw more than 4%?
Failure probability rises non-linearly. At 5% the historical success rate drops meaningfully and the first decade's returns start dominating the outcome; at 6% you're essentially gambling on sequence of returns. The rule's real lesson isn't the number 4 — it's that withdrawal rate, portfolio longevity, and market returns are locked together, and this page lets you move each lever.
Related calculators
Put the number in context with the FIRE number calculator and savings rate calculator, or browse everything at the FireVerdict hub.