Portfolio backtester

NOTE: this site is designed for desktop use. The interactive visualizations don't work well with a small screen and no mouse.

A free educational tool that uses 150 years of historical data across 16 countries to simulate how different asset portfolios perform in supporting retirement withdrawals. Everything is shown in today's money, adjusted using historical year-by-year inflation.

Inputs: Basics

10 yrs50 yrs
Your data is private. No financial data is ever transmitted to bcktstr.com or others.
▸ Export settings ▸ Import settings

Inputs: Withdrawals

£0.1m£10m
0%2%
£0£100k
£40k (gross) in year 1, grows with inflation each year.
Year 1 withdrawal is 4.0% of assets; this %ge varies yearly.
One-off or recurring, in today's money.
New: yr £ k
Reduced to 30%Not reduced
Affects any year that equities fall >15%.

Inputs: Allocation

Your mix
Cash 20% Bond 20% Gold 0% Equity 60%
Equity tilt is searched jointly with asset allocations (5% steps), then asset allocations are refined at 1%.
[?]
[?]

Analysis

Alternative mixes[?]
Ruin rate
—
tests where money ran out
vs min-ruin mix
—
your mix vs min-ruin mix
End wealth
—
Median
—
10%ile
Outcome by start year
Wealth path of each start year
Final wealth
Market statistics used
About this tool: This website is created and maintained by an individual UK-based investor. You can reach me at hi@bcktstr.com. Happy to hear from you if you find a bug, or have a feature request, or if you just found this useful.
Caveats — why not to rely on this: this tool uses real historical data for inflation, FX and asset performance. However, the future is not the past, it may be worse, better, or just different, and you should not rely on backtesting alone in your portfolio planning. The tool ignores all types of taxes (income, capital gains, inheritance, ...). The data is annual, so within-year swings are not modelled. No guarantee is made that the data or processing is accurate. This is a self-directed teaching instrument, not financial advice.
Privacy: the tool runs all computations locally in your browser, and settings stay in local storage on your device. No financial data is ever transmitted to anyone. Cloudflare (the hosting platform) collects aggregate visit and performance data only.
v4.0 · 8 July 2026 ▸ Run test suite ▸ Version history ▸ Data sources & licences