A thousand simulated futures for your mix, tested at every withdrawal rate and every horizon. The answer is the rate that still holds in 95 of 100 of them.
Stocks = MSCI ACWI · Bonds = US Aggregate · Cash = Money Market · 0.5% annual fee · Annual rebalancing
Configure your retirement setup above and click Calculate SWR.
Portfolio Lab includes 42 asset classes, 5 optimization methods, Monte Carlo fan charts, guardrails spending strategies, and 23 years of backtesting — all powered by J.P. Morgan data.
Try Portfolio Lab FreeA safe withdrawal rate answers “what can I spend so the money lasts N years?” A perpetual withdrawal rate answers a stricter question: “what can I spend so the portfolio never runs out — and ideally keeps its real value forever?” Perpetual rates matter for early retirees with 40+ year horizons, for endowment-style planning, and for anyone who wants to leave the principal intact. They typically sit 0.5–1.5 percentage points below a 30-year SWR.
In the heatmap above, the longest horizons at high confidence are a practical proxy for a perpetual rate: if a withdrawal rate survives 40 years at 95–99% confidence with forward-looking return assumptions, it is close to indefinitely sustainable. Because the calculator is currency-agnostic, the same framework works whether your portfolio is in dollars, pounds, or euros.
Using forward-looking capital market assumptions rather than historical averages, Monte Carlo simulation typically supports a 3.5-4.5% initial withdrawal rate for a diversified 30-year retirement at high confidence, depending on your stock/bond mix. Forward-looking assumptions matter: today's valuations and yields imply different sustainable rates than the historical averages behind the original 4% rule.
A perpetual withdrawal rate is the rate at which your portfolio is expected to sustain withdrawals indefinitely — preserving its real value rather than merely lasting a fixed number of years. It is always lower than a 30-year safe withdrawal rate, typically by 0.5-1.5 percentage points. In this calculator, the longest horizons at 95%+ confidence approximate a perpetual rate.
The 4% rule came from the Trinity Study, which used historical US stock and bond returns from 1926 onward. With today's forward-looking return estimates, 4% remains close to sustainable for a 30-year retirement with a balanced portfolio, but the confidence level is lower than the historical study implied. Testing your own mix with Monte Carlo simulation at your chosen confidence level is more robust than a fixed rule.
Yes — the calculator is currency-agnostic, so UK investors can enter portfolio values in pounds and read the withdrawal rates the same way, whether the portfolio sits in an ISA, SIPP, or taxable account. Note the underlying return assumptions are USD-based estimates, so treat the results as a framework rather than a precise GBP forecast.
A rate is one number. The workstation tests it against your actual holdings, with guardrails that cut spending when markets fall instead of hoping one rate holds for thirty years.
Open the workstation →