FAQ
Quick answers about how the calculator works and how to interpret results.
A common baseline is annual spending divided by a withdrawal rate such as 3.5% or 4%. This tool also shows plan resilience across historical windows because outcomes depend on market history and allocation.
The 4% rule is a rule of thumb that suggests withdrawing 4% of your portfolio per year, adjusted for inflation. It is a starting point, not a guarantee.
It can be a useful baseline, but UK taxes, inflation, and market sequences can change outcomes. A historical backtest is more informative than a fixed return assumption.
A safe withdrawal rate is a spending rate designed to last across difficult market periods. This calculator tests withdrawal rates across many historical windows.
The FI number is the estimated portfolio size required to sustain your spending without employment income. It is calculated using a baseline withdrawal rate and is shown alongside resilience results.
Plan resilience is the percentage of historical windows in which the plan remained sustainable for the full horizon. It is a stress test, not a forecast.
Yes, the calculator models tax-aware withdrawals across ISA, SIPP, and GIA using simplified UK tax rules. It is intended for planning rather than personal tax advice.
Yes, GIA withdrawals account for CGT in a simplified way based on gains and allowances. This helps estimate net spending delivered after tax.
Yes, you can set the annual amount and start age, and it reduces the withdrawal need once it begins.
Yes, you can add other annual income streams with a start age and an inflation adjustment toggle.
It runs the backtest using only data from 1970 onward. This is useful if you prefer to exclude earlier historical periods.
If your horizon is longer than the modern-era window, there are not enough years to run rolling historical scenarios. The tool warns you and shows the window length.
Yes, results are shown in inflation-adjusted terms so spending power is comparable across time.
Yes, even small annual fees compound over time. You can include an annual fee to reduce returns each year.
No. This is a historical backtest that shows how a plan would have performed across past market periods.
No, the calculator works without signup. Basic site analytics may be used to improve performance and usability.
Allocation depends on your risk tolerance and horizon. The presets are a starting point, and resilience results help compare tradeoffs.
The FI number is a baseline rule of thumb, while resilience reflects historical outcomes across many windows. Allocation and horizon can make resilience higher or lower than a simple rule suggests.
The best calculator is the one that matches your needs and assumptions. This tool is designed for UK users with tax-aware withdrawals and historical backtesting.
Start with the calculator, or read the methodology and data sources.
Last updated: 2026-02-23